JBoss Enterprise Application Platform 4.2

Hibernate Annotations Reference Guide

for Use with JBoss Enterprise Application Platform 4.2

Edition 1.0

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Hibernate Development Team

Edited by

Red Hat Inc. Engineering Content Services

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Abstract

This book is a Reference Guide to Hibernate Annotations for use with JBoss Enterprise Application Platform 4.2 and its patch releases.

Preface

1. Document Conventions

This manual uses several conventions to highlight certain words and phrases and draw attention to specific pieces of information.
In PDF and paper editions, this manual uses typefaces drawn from the Liberation Fonts set. The Liberation Fonts set is also used in HTML editions if the set is installed on your system. If not, alternative but equivalent typefaces are displayed. Note: Red Hat Enterprise Linux 5 and later include the Liberation Fonts set by default.

1.1. Typographic Conventions

Four typographic conventions are used to call attention to specific words and phrases. These conventions, and the circumstances they apply to, are as follows.
Mono-spaced Bold
Used to highlight system input, including shell commands, file names and paths. Also used to highlight keys and key combinations. For example:
To see the contents of the file my_next_bestselling_novel in your current working directory, enter the cat my_next_bestselling_novel command at the shell prompt and press Enter to execute the command.
The above includes a file name, a shell command and a key, all presented in mono-spaced bold and all distinguishable thanks to context.
Key combinations can be distinguished from an individual key by the plus sign that connects each part of a key combination. For example:
Press Enter to execute the command.
Press Ctrl+Alt+F2 to switch to a virtual terminal.
The first example highlights a particular key to press. The second example highlights a key combination: a set of three keys pressed simultaneously.
If source code is discussed, class names, methods, functions, variable names and returned values mentioned within a paragraph will be presented as above, in mono-spaced bold. For example:
File-related classes include filesystem for file systems, file for files, and dir for directories. Each class has its own associated set of permissions.
Proportional Bold
This denotes words or phrases encountered on a system, including application names; dialog box text; labeled buttons; check-box and radio button labels; menu titles and sub-menu titles. For example:
Choose SystemPreferencesMouse from the main menu bar to launch Mouse Preferences. In the Buttons tab, select the Left-handed mouse check box and click Close to switch the primary mouse button from the left to the right (making the mouse suitable for use in the left hand).
To insert a special character into a gedit file, choose ApplicationsAccessoriesCharacter Map from the main menu bar. Next, choose SearchFind… from the Character Map menu bar, type the name of the character in the Search field and click Next. The character you sought will be highlighted in the Character Table. Double-click this highlighted character to place it in the Text to copy field and then click the Copy button. Now switch back to your document and choose EditPaste from the gedit menu bar.
The above text includes application names; system-wide menu names and items; application-specific menu names; and buttons and text found within a GUI interface, all presented in proportional bold and all distinguishable by context.
Mono-spaced Bold Italic or Proportional Bold Italic
Whether mono-spaced bold or proportional bold, the addition of italics indicates replaceable or variable text. Italics denotes text you do not input literally or displayed text that changes depending on circumstance. For example:
To connect to a remote machine using ssh, type ssh username@domain.name at a shell prompt. If the remote machine is example.com and your username on that machine is john, type ssh john@example.com.
The mount -o remount file-system command remounts the named file system. For example, to remount the /home file system, the command is mount -o remount /home.
To see the version of a currently installed package, use the rpm -q package command. It will return a result as follows: package-version-release.
Note the words in bold italics above — username, domain.name, file-system, package, version and release. Each word is a placeholder, either for text you enter when issuing a command or for text displayed by the system.
Aside from standard usage for presenting the title of a work, italics denotes the first use of a new and important term. For example:
Publican is a DocBook publishing system.

1.2. Pull-quote Conventions

Terminal output and source code listings are set off visually from the surrounding text.
Output sent to a terminal is set in mono-spaced roman and presented thus:
books        Desktop   documentation  drafts  mss    photos   stuff  svn
books_tests  Desktop1  downloads      images  notes  scripts  svgs
Source-code listings are also set in mono-spaced roman but add syntax highlighting as follows:
package org.jboss.book.jca.ex1;

import javax.naming.InitialContext;

public class ExClient
{
   public static void main(String args[]) 
       throws Exception
   {
      InitialContext iniCtx = new InitialContext();
      Object         ref    = iniCtx.lookup("EchoBean");
      EchoHome       home   = (EchoHome) ref;
      Echo           echo   = home.create();

      System.out.println("Created Echo");

      System.out.println("Echo.echo('Hello') = " + echo.echo("Hello"));
   }
}

1.3. Notes and Warnings

Finally, we use three visual styles to draw attention to information that might otherwise be overlooked.

Note

Notes are tips, shortcuts or alternative approaches to the task at hand. Ignoring a note should have no negative consequences, but you might miss out on a trick that makes your life easier.

Important

Important boxes detail things that are easily missed: configuration changes that only apply to the current session, or services that need restarting before an update will apply. Ignoring a box labeled 'Important' will not cause data loss but may cause irritation and frustration.

Warning

Warnings should not be ignored. Ignoring warnings will most likely cause data loss.

2. Feedback

If you spot a typo in this guide, or if you have thought of a way to make this manual better, we would love to hear from you! Submit a report in JIRA against the Product: JBoss Enterprise Application Platform, Version: <version>, Component: Doc. If you have a suggestion for improving the documentation, try to be as specific as possible. If you have found an error, include the section number and some of the surrounding text so we can find it easily.

Chapter 1. Introduction

Hibernate, like all other object/relational mapping tools, requires metadata that governs the transformation of data from one representation to the other (and vice versa). In Hibernate 2.x, mapping metadata is most of the time declared in XML text files. Another option is XDoclet, utilizing Javadoc source code annotations and a preprocessor at compile time. The same kind of annotation support is now available in the standard JDK, although more powerful and better supported by tools. IntelliJ IDEA, and Eclipse for example, support auto-completion and syntax highlighting of JDK 5.0 annotations. Annotations are compiled into the bytecode and read at runtime (in Hibernate's case on startup) using reflection, so no external XML files are needed.
The EJB3 specification recognizes the interest in and the success of the transparent object/relational mapping paradigm. The EJB3 specification standardizes the basic APIs and the metadata needed for any object/relational persistence mechanism. Hibernate EntityManager implements the programming interfaces and lifecycle rules as defined by the EJB3 persistence specification. Together with Hibernate Annotations, this wrapper implements a complete (and standalone) EJB3 persistence solution on top of the mature Hibernate core. You may use a combination of all three together, annotations without EJB3 programming interfaces and lifecycle, or even pure native Hibernate, depending on the business and technical needs of your project. You can at all times fall back to Hibernate native APIs, or if required, even to native JDBC and SQL.
This release is based on the final release of the EJB 3.0 / JPA specification (aka JSP-220) and support all the specification features (including the optional ones). Most of the Hibernate features and extensions are also available through Hibernate-specific annotations compared to the specification are also available. While the Hibernate feature coverage is now very high, some are still missing. The eventual goal is to cover all of them. See the JIRA road map section for more information.
If you are moving from previous Hibernate Annotations versions, please have a look at Java Persistence migration guide.

Chapter 2. Setting up an annotations project

2.1. Requirements

  • Download and unpack the Hibernate Annotations distribution from the Hibernate website.
  • This release requires Hibernate Core 3.2.0.GA and above.
  • This release is known to work on Hibernate Core 3.2.0 up to 3.2.2.GA
  • Make sure you have JDK 5.0 installed or above. You can of course continue using XDoclet and get some of the benefits of annotation-based metadata with older JDK versions. Note that this document only describes JDK 5.0 annotations and you have to refer to the XDoclet documentation for more information.

2.2. Configuration

First, set up your classpath (after you have created a new project in your favorite IDE):
  • Copy all Hibernate3 core and required 3rd party library files (see lib/README.txt in Hibernate).
  • Copy hibernate-annotations.jar, lib/hibernate-comons-annotations.jar and lib/ejb3-persistence.jar from the Hibernate Annotations distribution to your classpath as well.
If you wish to use Hibernate Validator, download it from the Hibernate website and add hibernate-validator.jar in your classpath.
If you wish to use Hibernate Search, download it from the Hibernate website and add hibernate-search.jar and lucene-core-x.y.z.jar in your classpath.
We also recommend a small wrapper class to startup Hibernate in a static initializer block, known as HibernateUtil. You might have seen this class in various forms in other areas of the Hibernate documentation. For Annotation support you have to enhance this helper class as follows:
package hello;

import org.hibernate.*;
import org.hibernate.cfg.*;
import test.*;
import test.animals.Dog;

public class HibernateUtil {

private static final SessionFactory sessionFactory;

    static {
        try {

            sessionFactory = new AnnotationConfiguration()
                    configure().buildSessionFactory();
        } catch (Throwable ex) {
            // Log exception!
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static Session getSession()
            throws HibernateException {
        return sessionFactory.openSession();
    }
}
Interesting here is the use of AnnotationConfiguration. The packages and annotated classes are declared in your regular XML configuration file (usually hibernate.cfg.xml). Here is the equivalent of the above declaration:
<!DOCTYPE hibernate-configuration PUBLIC
  "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
  "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

  <hibernate-configuration>
    <session-factory>
      <mapping package="test.animals"/> 
      <mapping class="test.Flight"/> 
      <mapping class="test.Sky"/> 
      <mapping class="test.Person"/> 
      <mapping class="test.animals.Dog"/> 
      <mapping resource="test/animals/orm.xml"/>
    </session-factory>
  </hibernate-configuration>
Note that you can mix the hbm.xml use and the new annotation one. The resource element can be either an hbm file or an EJB3 XML deployment descriptor. The distinction is transparent for your configuration process.
Alternatively, you can define the annotated classes and packages using the programmatic API
sessionFactory = new AnnotationConfiguration() .addPackage("test.animals") 
/* the fully qualified package name 
 * .addAnnotatedClass(Flight.class) 
 * .addAnnotatedClass(Sky.class) 
 * .addAnnotatedClass(Person.class) 
 * .addAnnotatedClass(Dog.class)
 */
.addResource("test/animals/orm.xml")
configure()..buildSessionFactory();
You can also use the Hibernate EntityManager which has its own configuration mechanism. Please refer to this project documentation for more details.
There is no other difference in the way you use Hibernate APIs with annotations, except for this startup routine change or in the configuration file. You can use your favorite configuration method for other properties ( hibernate.properties, hibernate.cfg.xml, programmatic APIs, etc). You can even mix annotated persistent classes and classic hbm.cfg.xml declarations with the same SessionFactory. You can however not declare a class several times (whether annotated or through hbm.xml). You cannot mix configuration strategies (hbm vs annotations) in a mapped entity hierarchy either.
To ease the migration process from hbm files to annotations, the configuration mechanism detects the mapping duplication between annotations and hbm files. HBM files are then prioritized over annotated metadata on a class to class basis. You can change the priority using hibernate.mapping.precedence property. The default is hbm, class, changing it to class, hbm will prioritize the annotated classes over hbm files when a conflict occurs.

2.3. Properties

Aside from the Hibernate core properties, Hibernate Annotations reacts to the following one:
hibernate.validator.apply_to_ddl
Use Hibernate Validator annotations to refine the database schema generation. Default to true.

Chapter 3. Entity Beans

3.1. Intro

This section covers EJB 3.0 (aka Java Persistence) entity annotations and Hibernate-specific extensions.

3.2. Mapping with EJB3/JPA Annotations

EJB3 entities are plain POJOs. Actually they represent the exact same concept as the Hibernate persistent entities. Their mappings are defined through JDK 5.0 annotations (an XML descriptor syntax for overriding is defined in the EJB3 specification). Annotations can be split in two categories, the logical mapping annotations (allowing you to describe the object model, the class associations, etc.) and the physical mapping annotations (describing the physical schema, tables, columns, indexes, etc). We will mix annotations from both categories in the following code examples.
EJB3 annotations are in the javax.persistence.* package. Most JDK 5 compliant IDE (like Eclipse, IntelliJ IDEA and Netbeans) can autocomplete annotation interfaces and attributes for you (even without a specific "EJB3" module, since EJB3 annotations are plain JDK 5 annotations).
For more and runnable concrete examples read the JBoss EJB 3.0 tutorial or review the Hibernate Annotations test suite. Most of the unit tests have been designed to represent a concrete example and be a source of inspiration.

3.2.1. Declaring an entity bean

Every bound persistent POJO class is an entity bean and is declared using the @Entity annotation (at the class level):
@Entity
public class Flight implements Serializable {
    Long id;

    @Id
    public Long getId() { return id; }

    public void setId(Long id) { this.id = id; }
}
@Entity declares the class as an entity bean (i.e. a persistent POJO class), @Id declares the identifier property of this entity bean. The other mapping declarations are implicit. This "configuration by exception" concept is central to the new EJB3 specification and a major improvement. The class Flight is mapped to the Flight table, using the column id as its primary key column.
Depending on whether you annotate fields or methods, the access type used by Hibernate will be field or property. The EJB3 spec requires that you declare annotations on the element type that will be accessed, that is, the getter method if you use property access, the field if you use field access. Mixing EJB3 annotations in both fields and methods should be avoided. Hibernate will guess the access type from the position of @Id or @EmbeddedId.

3.2.1.1. Defining the table

@Table is set at the class level. It allows you to define the table, catalog, and schema names for your entity bean mapping. If no @Table is defined the default values are used: the unqualified class name of the entity.
@Entity
@Table(name="tbl_sky")
public class Sky implements Serializable {
...
The @Table element also contains schema and a catalog attributes, if they need to be defined. You can also define unique constraints to the table using the @UniqueConstraint annotation in conjunction with @Table (for a unique constraint bound to a single column, refer to @Column).
@Table(name="tbl_sky",
    uniqueConstraints = {@UniqueConstraint(columnNames={"month", "day"})}
)
A unique constraint is applied to the tuple month, day. Note that the columnNames array refers to the logical column names.

3.2.1.2. Versioning for optimistic locking

You can add optimistic locking capability to an entity bean using the @Version annotation:
@Entity
public class Flight implements Serializable {
...
    @Version
    @Column(name="OPTLOCK")
    public Integer getVersion() { ... }
}
The version property will be mapped to the OPTLOCK column, and the entity manager will use it to detect conflicting updates (preventing lost updates you might otherwise see with the last-commit-wins strategy).
The version column may be a numeric (the recommended solution) or a timestamp as per the EJB3 spec. Hibernate supports any kind of type provided that you define and implement the appropriate UserVersionType.
The application must not alter the version number set up by Hibernate in any way. To artificially increase the version number, check in Hibernate EntityManager's reference documentation LockMode.WRITE

3.2.2. Mapping simple properties

3.2.2.1. Declaring basic property mappings

Every non-static non-transient property (field or method) of an entity bean is considered persistent, unless you annotate it as @Transient. Not having an annotation for your property is equivalent to the appropriate @Basic annotation. The @Basic annotation allows you to declare the fetching strategy for a property:
public transient int counter; //transient property

private String firstname; //persistent property

@Transient
String getLengthInMeter() { ... } //transient property

String getName() {... } // persistent property

@Basic
int getLength() { ... } // persistent property

@Basic(fetch = FetchType.LAZY)
String getDetailedComment() { ... } // persistent property

@Temporal(TemporalType.TIME)
java.util.Date getDepartureTime() { ... } // persistent property           

@Enumerated(EnumType.STRING)
Starred getNote() { ... } //enum persisted as String in database
counter, a transient field, and lengthInMeter, a method annotated as @Transient, and will be ignored by the entity manager. name, length, and firstname properties are mapped persistent and eagerly fetched (the default for simple properties). The detailedComment property value will be lazily fetched from the database once a lazy property of the entity is accessed for the first time. Usually you don't need to lazy simple properties (not to be confused with lazy association fetching).

Note

To enable property-level lazy fetching, your classes have to be instrumented: bytecode is added to the original one to enable such feature – please refer to the Hibernate reference documentation. If your classes are not instrumented, property level lazy loading is silently ignored.
The recommended alternative is to use the projection capability of EJB-QL or Criteria queries.
EJB3 supports property mapping of all basic types supported by Hibernate (all basic Java types, their respective wrappers and serializable classes). Hibernate Annotations supports out-of-the-box Enum type mapping either into a ordinal column (saving the enum ordinal) or a string-based column (saving the enum string representation): the persistence representation, defaulted to ordinal, can be overridden through the @Enumerated annotation as shown in the note property example.
In core Java APIs, the temporal precision is not defined. When dealing with temporal data you might want to describe the expected precision in database. Temporal data can have DATE, TIME, or TIMESTAMP precision (ie the actual date, only the time, or both). Use the @Temporal annotation to fine tune that.
@Lob indicates that the property should be persisted in a Blob or a Clob depending on the property type: java.sql.Clob, Character[], char[] and java.lang.String will be persisted in a Clob. java.sql.Blob, Byte[], byte[] and serializable type will be persisted in a Blob.
@Lob
public String getFullText() {
    return fullText;
}

@Lob 
public byte[] getFullCode() {
    return fullCode;
}
If the property type implements java.io.Serializable and is not a basic type, and if the property is not annotated with @Lob, then the Hibernate serializable type is used.

3.2.2.2. Declaring column attributes

The column(s) used for a property mapping can be defined using the @Column annotation. Use it to override default values (see the EJB3 specification for more information on the defaults). You can use this annotation at the property level for properties that are:
  • not annotated at all
  • annotated with @Basic
  • annotated with @Version
  • annotated with @Lob
  • annotated with @Temporal
  • annotated with @org.hibernate.annotations.CollectionOfElements (for Hibernate only)
@Entity
public class Flight implements Serializable {
...
@Column(updatable = false, name = "flight_name", nullable = false, length=50)
public String getName() { ... }
The name property is mapped to the flight_name column, which is not nullable, has a length of 50 and is not updatable (making the property immutable).
This annotation can be applied to regular properties as well as @Id or @Version properties.
@Column(
    name="columnName";
    boolean unique() default false;
    boolean nullable() default true;
    boolean insertable() default true;
    boolean updatable() default true;
    String columnDefinition() default "";
    String table() default "";
    int length() default 255;
    int precision() default 0; // decimal precision
    int scale() default 0; // decimal scale

Notes

  1. name (optional): the column name (default to the property name)
  2. unique (optional): set a unique constraint on this column or not (default false)
  3. nullable (optional): set the column as nullable (default true).
  4. insertable (optional): whether or not the column will be part of the insert statement (default true)
  5. updatable (optional): whether or not the column will be part of the update statement (default true)
  6. columnDefinition (optional): override the sql DDL fragment for this particular column (non portable)
  7. table (optional): define the targeted table (default primary table)
  8. length (optional): column length (default 255)
  9. precision (optional): column decimal precision (default 0)
  10. scale (optional): column decimal scale if useful (default 0)

3.2.2.3. Embedded objects (aka components)

It is possible to declare an embedded component inside an entity and even override its column mapping. Component classes have to be annotated at the class level with the @Embeddable annotation. It is possible to override the column mapping of an embedded object for a particular entity using the @Embedded and @AttributeOverride annotation in the associated property:
@Entity
public class Person implements Serializable {

    // Persistent component using defaults
    Address homeAddress;

    @Embedded
    @AttributeOverrides( {
            @AttributeOverride(name="iso2", column = @Column(name="bornIso2") ),
            @AttributeOverride(name="name", column = @Column(name="bornCountryName") )
    } )
    Country bornIn;
    ...
}
@Embeddable
public class Address implements Serializable {
    String city;
    Country nationality; //no overriding here
}
@Embeddable
public class Country implements Serializable {
    private String iso2;
    @Column(name="countryName") private String name;

    public String getIso2() { return iso2; }
    public void setIso2(String iso2) { this.iso2 = iso2; }

    
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    ...
}
A embeddable object inherits the access type of its owning entity (note that you can override that using the Hibernate-specific @AccessType annotations (see Section 3.4, “Hibernate Annotation Extensions”).
The Person entity bean has two component properties, homeAddress and bornIn. homeAddress property has not been annotated, but Hibernate will guess that it is a persistent component by looking for the @Embeddable annotation in the Address class. We also override the mapping of a column name (to bornCountryName) with the @Embedded and @AttributeOverride annotations for each mapped attribute of Country. As you can see, Country is also a nested component of Address, again using auto-detection by Hibernate and EJB3 defaults. Overriding columns of embedded objects of embedded objects is currently not supported in the EJB3 spec, however, Hibernate Annotations supports it through dotted expressions.
@Embedded
    @AttributeOverrides( {
            @AttributeOverride(name="city", column = @Column(name="fld_city") ),
            @AttributeOverride(name="nationality.iso2", column = @Column(name="nat_Iso2") ),
            @AttributeOverride(name="nationality.name", column = @Column(name="nat_CountryName") )
            //nationality columns in homeAddress are overridden
    } )
    Address homeAddress;
Hibernate Annotations supports one more feature that is not explicitly supported by the EJB3 specification: you can annotate a embedded object with the @MappedSuperclass annotation to make the superclass properties persistent (see @MappedSuperclass for more information).
While not supported by the EJB3 specification, Hibernate Annotations allows you to use association annotations in an embeddable object (ie @*ToOne nor @*ToMany). To override the association columns you can use @AssociationOverride.
If you want to have the same embeddable object type twice in the same entity, the column name defaulting will not work: at least one of the columns will have to be explicit. Hibernate goes beyond the EJB3 spec and allows you to enhance the defaulting mechanism through the NamingStrategy. DefaultComponentSafeNamingStrategy is a small improvement over the default EJB3NamingStrategy that allows embedded objects to be defaulted even if used twice in the same entity.

3.2.2.4. Non-annotated property defaults

If a property is not annotated, the following rules apply:
  • If the property is of a single type, it is mapped as @Basic
  • Otherwise, if the type of the property is annotated as @Embeddable, it is mapped as @Embedded
  • Otherwise, if the type of the property is Serializable, it is mapped as @Basic in a column holding the object in its serialized version
  • Otherwise, if the type of the property is java.sql.Clob or java.sql.Blob, it is mapped as @Lob with the appropriate LobType

3.2.3. Mapping identifier properties

The @Id annotation lets you define which property is the identifier of your entity bean. This property can be set by the application itself or be generated by Hibernate (preferred). You can define the identifier generation strategy thanks to the @GeneratedValue annotation:
AUTO>
identity column, sequence or table depending on the underlying DB
TABLE>
table holding the id
IDENTITY>
identity column
SEQUENCE>
sequence
Hibernate provides more id generators than the basic EJB3 ones. Check Section 3.4, “Hibernate Annotation Extensions” for more information.
The following example shows a sequence generator using the SEQ_STORE configuration (see below)
@Id @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="SEQ_STORE")
public Integer getId() { ... }
The next example uses the identity generator:
@Id @GeneratedValue(strategy=GenerationType.IDENTITY)
public Long getId() { ... }
The AUTO generator is the preferred type for portable applications (across several DB vendors). The identifier generation configuration can be shared for several @Id mappings with the generator attribute. There are several configurations available through @SequenceGenerator and @TableGenerator. The scope of a generator can be the application or the class. Class-defined generators are not visible outside the class and can override application level generators. Application-level generators are defined at XML level (see Chapter 4, Overriding metadata through XML):
<table-generator name="EMP_GEN"
            table="GENERATOR_TABLE"
            pk-column-name="key"
            value-column-name="hi"
            pk-column-value="EMP"
            allocation-size="20"/>

//and the annotation equivalent

@javax.persistence.TableGenerator(
    name="EMP_GEN",
    table="GENERATOR_TABLE",
    pkColumnName = "key",
    valueColumnName = "hi"
    pkColumnValue="EMP",
    allocationSize=20
)

<sequence-generator name="SEQ_GEN" 
    sequence-name="my_sequence"
    allocation-size="20"/>

//and the annotation equivalent

@javax.persistence.SequenceGenerator(
    name="SEQ_GEN",
    sequenceName="my_sequence",
    allocationSize=20
)
If JPA XML (like META-INF/orm.xml) is used to define the generators, EMP_GEN and SEQ_GEN are application level generators. EMP_GEN defines a table based id generator using the hilo algorithm with a max_lo of 20. The hi value is kept in a table "GENERATOR_TABLE". The information is kept in a row where pkColumnName "key" is equals to pkColumnValue "EMP" and column valueColumnName "hi" contains the the next high value used.
SEQ_GEN defines a sequence generator using a sequence named my_sequence. The allocation size used for this sequence based hilo algorithm is 20. Note that this version of Hibernate Annotations does not handle initialValue in the sequence generator. The default allocation size is 50, so if you want to use a sequence and pickup the value each time, you must set the allocation size to 1.

Note

Package level definition is no longer supported by the EJB 3.0 specification. However, you can use the @GenericGenerator at the package level (see Section 3.4.Identifier, “Identifier”).
The next example shows the definition of a sequence generator in a class scope:
@Entity
@javax.persistence.SequenceGenerator(
    name="SEQ_STORE",
    sequenceName="my_sequence"
)
public class Store implements Serializable {
    private Long id;

    @Id @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="SEQ_STORE")
    public Long getId() { return id; }
}
This class will use a sequence named my_sequence and the SEQ_STORE generator is not visible in other classes. Note that you can check the Hibernate Annotations tests in the org.hibernate.test.annotations.id package for more examples.
You can define a composite primary key through several syntaxes:
  • annotate the component property as @Id and make the component class @Embeddable
  • annotate the component property as @EmbeddedId
  • annotate the class as @IdClass and annotate each property of the entity involved in the primary key with @Id
While quite common to the EJB2 developer, @IdClass is likely new for Hibernate users. The composite primary key class corresponds to multiple fields or properties of the entity class, and the names of primary key fields or properties in the primary key class and those of the entity class must match and their types must be the same. Let's look at an example:
@Entity
@IdClass(FootballerPk.class)
public class Footballer {
    //part of the id key
    @Id public String getFirstname() {
        return firstname;
    }

    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }

    //part of the id key
    @Id public String getLastname() {
        return lastname;
    }

    public void setLastname(String lastname) {
        this.lastname = lastname;
    }

    public String getClub() {
        return club;
    }

    public void setClub(String club) {
        this.club = club;
    }

    //appropriate equals() and hashCode() implementation
}

@Embeddable
public class FootballerPk implements Serializable {
    //same name and type as in Footballer
    public String getFirstname() {
        return firstname;
    }

    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }

    //same name and type as in Footballer
    public String getLastname() {
        return lastname;
    }

    public void setLastname(String lastname) {
        this.lastname = lastname;
    }

    //appropriate equals() and hashCode() implementation
}
As you may have seen, @IdClass points to the corresponding primary key class.
While not supported by the EJB3 specification, Hibernate allows you to define associations inside a composite identifier. Simply use the regular annotations for that.
@Entity
@AssociationOverride( name="id.channel", joinColumns = @JoinColumn(name="chan_id") )
public class TvMagazin {
    @EmbeddedId public TvMagazinPk id;
    @Temporal(TemporalType.TIME) Date time;
}

@Embeddable
public class TvMagazinPk implements Serializable {
    @ManyToOne
    public Channel channel;
    public String name;
    @ManyToOne
    public Presenter presenter;
}

3.2.4. Mapping inheritance

EJB3 supports the three types of inheritance:
  • Table per Class Strategy: the <union-class> element in Hibernate
  • Single Table per Class Hierarchy Strategy: the <subclass> element in Hibernate
  • Joined Subclass Strategy: the <joined-subclass> element in Hibernate
The chosen strategy is declared at the class level of the top level entity in the hierarchy using the @Inheritance annotation.

Note

Annotating interfaces is currently not supported.

3.2.4.1. Table per class

This strategy has many drawbacks (esp. with polymorphic queries and associations) explained in the EJB3 spec, the Hibernate reference documentation, Hibernate in Action, and many other places. Hibernate works around most of them implementing this strategy using SQL UNION queries. It is commonly used for the top level of an inheritance hierarchy:
@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class Flight implements Serializable {
This strategy supports one-to-many associations provided that they are bidirectional. This strategy does not support the IDENTITY generator strategy: the id has to be shared across several tables. Consequently, when using this strategy, you should not use AUTO nor IDENTITY.

3.2.4.2. Single table per class hierarchy

All properties of all super- and subclasses are mapped into the same table, instances are distinguished by a special discriminator column:
@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(
    name="planetype",
    discriminatorType=DiscriminatorType.STRING
)
@DiscriminatorValue("Plane")
public class Plane { ... }

@Entity
@DiscriminatorValue("A320")
public class A320 extends Plane { ... }
Plane is the superclass, it defines the inheritance strategy InheritanceType.SINGLE_TABLE. It also defines the discriminator column through the @DiscriminatorColumn annotation. A discriminator column can also define the discriminator type. Finally, the @DiscriminatorValue annotation defines the value used to differentiate a class in the hierarchy. All of these attributes have sensible default values. The default name of the discriminator column is DTYPE. The default discriminator value is the entity name (as defined in @Entity.name) for DiscriminatorType.STRING. A320 is a subclass; you only have to define discriminator value if you don't want to use the default value. The strategy and the discriminator type are implicit.
@Inheritance and @DiscriminatorColumn should only be defined at the top of the entity hierarchy.

3.2.4.3. Joined subclasses

The @PrimaryKeyJoinColumn and @PrimaryKeyJoinColumns annotations define the primary key(s) of the joined subclass table:
@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public class Boat implements Serializable { ... }

@Entity
public class Ferry extends Boat { ... }

@Entity
@PrimaryKeyJoinColumn(name="BOAT_ID")
public class AmericaCupClass  extends Boat { ... }
All of the above entities use the JOINED strategy, the Ferry table is joined with the Boat table using the same primary key names. The AmericaCupClass table is joined with Boat using the join condition Boat.id = AmericaCupClass.BOAT_ID.

3.2.4.4. Inherit properties from superclasses

This is sometimes useful to share common properties through a technical or a business superclass without including it as a regular mapped entity (ie no specific table for this entity). For that purpose you can map them as @MappedSuperclass.
@MappedSuperclass
public class BaseEntity {
    @Basic
    @Temporal(TemporalType.TIMESTAMP)
    public Date getLastUpdate() { ... }
    public String getLastUpdater() { ... }
    ...
}

@Entity class Order extends BaseEntity {
    @Id public Integer getId() { ... }
    ...
}
In database, this hierarchy will be represented as an Order table having the id, lastUpdate and lastUpdater columns. The embedded superclass property mappings are copied into their entity subclasses. Remember that the embeddable superclass is not the root of the hierarchy though.

Note

Properties from superclasses not mapped as @MappedSuperclass are ignored.

Note

The access type (field or methods), is inherited from the root entity, unless you use the Hibernate annotation @AccessType

Note

The same notion can be applied to @Embeddable objects to persist properties from their superclasses. You also need to use @MappedSuperclass to do that (this should not be considered as a standard EJB3 feature though)

Note

It is allowed to mark a class as @MappedSuperclass in the middle of the mapped inheritance hierarchy.

Note

Any class in the hierarchy non annotated with @MappedSuperclass nor @Entity will be ignored.
You can override columns defined in entity superclasses at the root entity level using the @AttributeOverride annotation.
@MappedSuperclass
public class FlyingObject implements Serializable {

    public int getAltitude() {
        return altitude;
    }

    @Transient
    public int getMetricAltitude() {
        return metricAltitude;
    }

    @ManyToOne
    public PropulsionType getPropulsion() {
        return metricAltitude;
    }
    ...
}

@Entity
@AttributeOverride( name="altitude", column = @Column(name="fld_altitude") )
@AssociationOverride( name="propulsion", joinColumns = @JoinColumn(name="fld_propulsion_fk") )
public class Plane extends FlyingObject {
    ...
}
The altitude property will be persisted in an fld_altitude column of table Plane and the propulsion association will be materialized in a fld_propulsion_fk foreign key column.
You can define @AttributeOverride(s) and @AssociationOverride(s) on @Entity classes, @MappedSuperclass classes and properties pointing to an @Embeddable object.

3.2.5. Mapping entity bean associations/relationships

3.2.5.1. One-to-one

You can associate entity beans through a one-to-one relationship using @OneToOne. There are three cases for one-to-one associations: either the associated entities share the same primary key values, a foreign key is held by one of the entities (note that this FK column in the database should be constrained unique to simulate one-to-one multiplicity), or an association table is used to store the link between the 2 entities (a unique constraint has to be defined on each fk to ensure the one-to-one multiplicity)
First, we map a real one-to-one association using shared primary keys:
@Entity
public class Body {
    @Id
    public Long getId() { return id; }

    @OneToOne(cascade = CascadeType.ALL)
    @PrimaryKeyJoinColumn
    public Heart getHeart() {
        return heart;
    }
    ...
}
@Entity
public class Heart {
    @Id
    public Long getId() { ...}
}
The one-to-one is marked as true by using the @PrimaryKeyJoinColumn annotation.
In the following example, the associated entities are linked through a foreign key column:
@Entity
public class Customer implements Serializable {
    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name="passport_fk")
    public Passport getPassport() {
        ...
    }

@Entity
public class Passport implements Serializable {
    @OneToOne(mappedBy = "passport")
    public Customer getOwner() {
    ...
}
A Customer is linked to a Passport, with a foreign key column named passport_fk in the Customer table. The join column is declared with the @JoinColumn annotation which looks like the @Column annotation. It has one more parameters named referencedColumnName. This parameter declares the column in the targeted entity that will be used to the join. Note that when using referencedColumnName to a non primary key column, the associated class has to be Serializable. Also note that the referencedColumnName to a non primary key column has to be mapped to a property having a single column (other cases might not work).
The association may be bidirectional. In a bidirectional relationship, one of the sides (and only one) has to be the owner: the owner is responsible for the association column(s) update. To declare a side as not responsible for the relationship, the attribute mappedBy is used. mappedBy refers to the property name of the association on the owner side. In our case, this is passport. As you can see, you must not declare the join column since it has already been declared on the owners side.
If no @JoinColumn is declared on the owner side, the defaults apply. A join column(s) will be created in the owner table and its name will be the concatenation of the name of the relationship in the owner side, _ (underscore), and the name of the primary key column(s) in the owned side. In this example passport_id because the property name is passport and the column id of Passport is id.
The third possibility (using an association table) is very exotic.
@Entity
public class Customer implements Serializable {
    @OneToOne(cascade = CascadeType.ALL)
    @JoinTable(name = "CustomerPassports", joinColumns = @JoinColumn(name="customer_fk"), inverseJoinColumns = @JoinColumn(name="passport_fk")
    )
    public Passport getPassport() {
        ...
    }

@Entity
public class Passport implements Serializable {
    @OneToOne(mappedBy = "passport")
    public Customer getOwner() {
    ...
}
A Customer is linked to a Passport through a association table named CustomerPassports ; this association table has a foreign key column named passport_fk pointing to the Passport table (materialized by the inverseJoinColumn and a foreign key column named customer_fk pointing to the Customer table materialized by the joinColumns attribute.
You must declare the join table name and the join columns explicitly in such a mapping.

3.2.5.2. Many-to-one

Many-to-one associations are declared at the property level with the annotation @ManyToOne:
@Entity()
public class Flight implements Serializable {
    @ManyToOne( cascade = {CascadeType.PERSIST, CascadeType.MERGE} )
    @JoinColumn(name="COMP_ID")
    public Company getCompany() {
        return company;
    }
    ...
}
The @JoinColumn attribute is optional, the default value(s) is like in one-to-one, the concatenation of the name of the relationship in the owner side, _ (underscore), and the name of the primary key column in the owned side. In this example company_id because the property name is company and the column id of Company is id.
@ManyToOne has a parameter named targetEntity which describes the target entity name. You usually don't need this parameter since the default value (the type of the property that stores the association) is good in almost all cases. However this is useful when you want to use interfaces as the return type instead of the regular entity.
@Entity()
public class Flight implements Serializable {
    @ManyToOne( cascade = {CascadeType.PERSIST, CascadeType.MERGE}, targetEntity=CompanyImpl.class )
    @JoinColumn(name="COMP_ID")
    public Company getCompany() {
        return company;
    }
    ...
}

public interface Company {
    ...
You can also map a many-to-one association through an association table. This association table described by the @JoinTable annotation will contains a foreign key referencing back the entity table (through @JoinTable.joinColumns) and a foreign key referencing the target entity table (through @JoinTable.inverseJoinColumns).
@Entity()
public class Flight implements Serializable {
    @ManyToOne( cascade = {CascadeType.PERSIST, CascadeType.MERGE} )
    @JoinTable(name="Flight_Company", joinColumns = @JoinColumn(name="FLIGHT_ID"), inverseJoinColumns = @JoinColumn(name="COMP_ID") )
    public Company getCompany() {
        return company;
    }
    ...
}

3.2.5.3. Collections

3.2.5.3.1. Overview
You can map Collection, List (ie ordered lists, not indexed lists), Map and Set. The EJB3 specification describes how to map an ordered list (that is, a list ordered at load time) using @javax.persistence.OrderBy annotation: this annotation takes into parameter a list of comma separated (target entity) properties to order the collection by (for example, firstname asc, age desc), if the string is empty, the collection will be ordered by id. For true indexed collections, please refer to the Section 3.4, “Hibernate Annotation Extensions”. EJB3 allows you to map Maps using as a key one of the target entity property using @MapKey(name="myProperty") (myProperty is a property name in the target entity). When using @MapKey (without property name), the target entity primary key is used. The map key uses the same column as the property pointed out: there is no additional column defined to hold the map key, and it does make sense since the map key actually represents a target property. Be aware that once loaded, the key is no longer kept in sync with the property, in other words, if you change the property value, the key will not change automatically in your Java model (for true map support please refers to Section 3.4, “Hibernate Annotation Extensions”). Many people confuse <map> capabilities and @MapKey ones. These are two different features. @MapKey still has some limitations, please check the forum or the JIRA tracking system for more information.
Hibernate has several notions of collections.

Table 3.1. Collections semantics

Semantic java representation annotations
Bag semantic java.util.List, java.util.Collection @org.hibernate.annotations.CollectionOfElements or @OneToMany or @ManyToMany
Bag semantic with primary key (without the limitations of Bag semantic) java.util.List, java.util.Collection (@org.hibernate.annotations.CollectionOfElements or @OneToMany or @ManyToMany) and @CollectionId
List semantic java.util.List (@org.hibernate.annotations.CollectionOfElements or @OneToMany or @ManyToMany) and @org.hibernate.annotations.IndexColumn
Set semantic java.util.Set @org.hibernate.annotations.CollectionOfElements or @OneToMany or @ManyToMany
Map semantic java.util.Map (@org.hibernate.annotations.CollectionOfElements or @OneToMany or @ManyToMany) and (nothing or @org.hibernate.annotations.MapKey/MapKeyManyToMany for true map support, OR @javax.persistence.MapKey

Collection of primitive, core type or embedded objects is not supported by the EJB3 specification. Hibernate Annotations allows them however (see Section 3.4, “Hibernate Annotation Extensions”).
@Entity public class City {
    @OneToMany(mappedBy="city")
    @OrderBy("streetName")
    public List<Street> getStreets() {
        return streets;
    }
...
}

@Entity public class Street {
    public String getStreetName() {
        return streetName;
    }

    @ManyToOne
    public City getCity() {
        return city;
    }
    ...
}


@Entity
public class Software {
    @OneToMany(mappedBy="software")
    @MapKey(name="codeName")
    public Map<String, Version> getVersions() {
        return versions;
    }
...
}

@Entity
@Table(name="tbl_version")
public class Version {
    public String getCodeName() {...}

    @ManyToOne
    public Software getSoftware() { ... }
...
}
So City has a collection of Streets that are ordered by streetName (of Street) when the collection is loaded. Software has a map of Versions which key is the Version codeName.
Unless the collection is a generic, you will have to define targetEntity. This is an annotation attribute that take the target entity class as a value.
3.2.5.3.2. One-to-many
One-to-many associations are declared at the property level with the annotation @OneToMany. One to many associations may be bidirectional.
3.2.5.3.2.1. Bidirectional
Since many-to-one are (almost) always the owner side of a bidirectional relationship in the EJB3 spec, the one-to-many association is annotated by @OneToMany( mappedBy=... )
@Entity
public class Troop {
    @OneToMany(mappedBy="troop")
    public Set<Soldier> getSoldiers() {
    ...
}

@Entity
public class Soldier {
    @ManyToOne
    @JoinColumn(name="troop_fk")
    public Troop getTroop() {
    ...
}
Troop has a bidirectional one-to-many relationship with Soldier through the troop property. You must not define any physical mapping in the mappedBy side.
To map a bidirectional one-to-many, with the one-to-many side as the owning side, you have to remove the mappedBy element and set the many-to-one @JoinColumn as insertable and updatable to false. This solution is obviously not optimized and will produce some additional UPDATE statements.
@Entity
public class Troop {
    @OneToMany
    @JoinColumn(name="troop_fk") //we need to duplicate the physical information
    public Set<Soldier> getSoldiers() {
    ...
}

@Entity
public class Soldier {
    @ManyToOne
    @JoinColumn(name="troop_fk", insertable=false, updatable=false)
    public Troop getTroop() {
    ...
}
3.2.5.3.2.2. Unidirectional
A unidirectional one-to-many using a foreign key column in the owned entity is not that common and not really recommended. We strongly advise you to use a join table for this kind of association (as explained in the next section). This kind of association is described through a @JoinColumn
@Entity
public class Customer implements Serializable {
    @OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER)
    @JoinColumn(name="CUST_ID")
    public Set<Ticket> getTickets() {
    ...
}

@Entity
public class Ticket implements Serializable {
    ... //no bidir
}
Customer describes a unidirectional relationship with Ticket using the join column CUST_ID.
3.2.5.3.2.3. Unidirectional with join table
A unidirectional one-to-many with join table is much preferred. This association is described through an @JoinTable.
@Entity
public class Trainer {
    @OneToMany
    @JoinTable(
            name="TrainedMonkeys",
            joinColumns = @JoinColumn( name="trainer_id"),
            inverseJoinColumns = @JoinColumn( name="monkey_id")
    )
    public Set<Monkey> getTrainedMonkeys() {
    ...
}

@Entity
public class Monkey {
    ... //no bidir
}
Trainer describes a unidirectional relationship with Monkey using the join table TrainedMonkeys, with a foreign key trainer_id to Trainer (joinColumns) and a foreign key monkey_id to Monkey (inversejoinColumns).
3.2.5.3.2.4. Defaults
Without describing any physical mapping, a unidirectional one-to-many with join table is used. The table name is the concatenation of the owner table name, _, and the other side table name. The foreign key name(s) referencing the owner table is the concatenation of the owner table, _, and the owner primary key column(s) name. The foreign key name(s) referencing the other side is the concatenation of the owner property name, _, and the other side primary key column(s) name. A unique constraint is added to the foreign key referencing the other side table to reflect the one-to-many.
@Entity
public class Trainer {
    @OneToMany
    public Set<Tiger> getTrainedTigers() {
    ...
}

@Entity
public class Tiger {
    ... //no bidir
}
Trainer describes a unidirectional relationship with Tiger using the join table Trainer_Tiger, with a foreign key trainer_id to Trainer (table name, _, trainer id) and a foreign key trainedTigers_id to Monkey (property name, _, Tiger primary column).
3.2.5.3.3. Many-to-many
3.2.5.3.3.1. Definition
A many-to-many association is defined logically using the @ManyToMany annotation. You also have to describe the association table and the join conditions using the @JoinTable annotation. If the association is bidirectional, one side has to be the owner and one side has to be the inverse end (ie. it will be ignored when updating the relationship values in the association table):
@Entity
public class Employer implements Serializable {
    @ManyToMany(
        targetEntity=org.hibernate.test.metadata.manytomany.Employee.class,
        cascade={CascadeType.PERSIST, CascadeType.MERGE}
    )
    @JoinTable(
        name="EMPLOYER_EMPLOYEE",
        joinColumns=@JoinColumn(name="EMPER_ID"),
        inverseJoinColumns=@JoinColumn(name="EMPEE_ID")
    )
    public Collection getEmployees() {
        return employees;
    }
    ...
}
@Entity
public class Employee implements Serializable {
    @ManyToMany(
        cascade = {CascadeType.PERSIST, CascadeType.MERGE},
        mappedBy = "employees",
        targetEntity = Employer.class
    )
    public Collection getEmployers() {
        return employers;
    }
}
We've already shown the many declarations and the detailed attributes for associations. We'll go deeper in the @JoinTable description, it defines a name, an array of join columns (an array in annotation is defined using { A, B, C }), and an array of inverse join columns. The latter ones are the columns of the association table which refer to the Employee primary key (the "other side").
As seen previously, the other side must not describe the physical mapping: a simple mappedBy argument containing the owner side property name bind the two.
3.2.5.3.3.2. Default values
As any other annotations, most values are guessed in a many-to-many relationship. Without describing any physical mapping in a unidirectional many-to-many the following rules applied. The table name is the concatenation of the owner table name, _ and the other side table name. The foreign key name(s) referencing the owner table is the concatenation of the owner table name, _ and the owner primary key column(s). The foreign key name(s) referencing the other side is the concatenation of the owner property name, _, and the other side primary key column(s). These are the same rules used for a unidirectional one-to-many relationship.
@Entity
public class Store {
    @ManyToMany(cascade = CascadeType.PERSIST)
    public Set<City> getImplantedIn() {
        ...
    }
}

@Entity
public class City {
    ... //no bidirectional relationship
}
A Store_City is used as the join table. The Store_id column is a foreign key to the Store table. The implantedIn_id column is a foreign key to the City table.
Without describing any physical mapping in a bidirectional many-to-many the following rules applied. The table name is the concatenation of the owner table name, _ and the other side table name. The foreign key name(s) referencing the owner table is the concatenation of the other side property name, _, and the owner primary key column(s). The foreign key name(s) referencing the other side is the concatenation of the owner property name, _, and the other side primary key column(s). These are the same rules used for a unidirectional one-to-many relationship.
@Entity
public class Store {
    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    public Set<Customer> getCustomers() {
        ...
    }
}

@Entity
public class Customer {
    @ManyToMany(mappedBy="customers")
    public Set<Store> getStores() {
        ...
    }
}
A Store_Customer is used as the join table. The stores_id column is a foreign key to the Store table. The customers_id column is a foreign key to the Customer table.

3.2.5.4. Transitive persistence with cascading

You probably have noticed the cascade attribute taking an array of CascadeType as a value. The cascade concept in EJB3 is very is similar to the transitive persistence and cascading of operations in Hibernate, but with slightly different semantics and cascading types:
  • CascadeType.PERSIST: cascades the persist (create) operation to associated entities persist() is called or if the entity is managed
  • CascadeType.MERGE: cascades the merge operation to associated entities if merge() is called or if the entity is managed
  • CascadeType.REMOVE: cascades the remove operation to associated entities if delete() is called
  • CascadeType.REFRESH: cascades the refresh operation to associated entities if refresh() is called
  • CascadeType.ALL: all of the above

Note

CascadeType.ALL also covers Hibernate-specific operations like save-update, lock etc... Check Section 3.4.7, “Cascade” for more information.
Please refer to the chapter 6.3 of the EJB3 specification for more information on cascading and create/merge semantics.

3.2.5.5. Association fetching

You have the ability to either eagerly or lazily fetch associated entities. The fetch parameter can be set to FetchType.LAZY or FetchType.EAGER. EAGER will try to use an outer join select to retrieve the associated object, while LAZY will only trigger a select when the associated object is accessed for the first time. @OneToMany and @ManyToMany associations are defaulted to LAZY and @OneToOne and @ManyToOne are defaulted to EAGER. For more information about static fetching, check Section 3.4.5.1, “Lazy options and fetching modes”.
The recommended approach is to use LAZY on all static fetching definitions and override this choice dynamically through JPA-QL. JPA-QL has a fetch keyword that allows you to override laziness when doing a particular query. This is very useful to improve performance and is decided on a use-case-to-use-case basis.

3.2.6. Mapping composite primary and foreign keys

Composite primary keys use a embedded class as the primary key representation, so you'd use the @Id and @Embeddable annotations. Alternatively, you can use the @EmbeddedId annotation. Note that the dependent class has to be serializable and implements equals()/hashCode(). You can also use @IdClass as described in Section 3.2.3, “Mapping identifier properties”.
@Entity
public class RegionalArticle implements Serializable {

    @Id
    public RegionalArticlePk getPk() { ... }
}

@Embeddable
public class RegionalArticlePk implements Serializable { ... }
or alternatively
@Entity
public class RegionalArticle implements Serializable {

    @EmbeddedId
    public RegionalArticlePk getPk() { ... }
}

public class RegionalArticlePk implements Serializable { ... }
@Embeddable inherits the access type of its owning entity unless the Hibernate-specific annotation @AccessType is used. Composite foreign keys (if not using the default sensitive values) are defined on associations using the @JoinColumns element, which is basically an array of @JoinColumn. It is considered a good practice to express referencedColumnNames explicitly. Otherwise, Hibernate will suppose that you use the same order of columns as in the primary key declaration.
@Entity
public class Parent implements Serializable {
    @Id
    public ParentPk id;
    public int age;

    @OneToMany(cascade=CascadeType.ALL)
    @JoinColumns ({
        @JoinColumn(name="parentCivility", referencedColumnName = "isMale"),
        @JoinColumn(name="parentLastName", referencedColumnName = "lastName"),
        @JoinColumn(name="parentFirstName", referencedColumnName = "firstName")
    })
    public Set<Child> children; //unidirectional
    ...
}
@Entity
public class Child implements Serializable {
    @Id @GeneratedValue
    public Integer id;

    @ManyToOne
    @JoinColumns ({
        @JoinColumn(name="parentCivility", referencedColumnName = "isMale"),
        @JoinColumn(name="parentLastName", referencedColumnName = "lastName"),
        @JoinColumn(name="parentFirstName", referencedColumnName = "firstName")
    })
    public Parent parent; //unidirectional
}
@Embeddable
public class ParentPk implements Serializable {
    String firstName;
    String lastName;
    ...
}
Note the explicit usage of the referencedColumnName.

3.2.7. Mapping secondary tables

You can map a single entity bean to several tables using the @SecondaryTable or @SecondaryTables class level annotations. To express that a column is in a particular table, use the table parameter of @Column or @JoinColumn.
@Entity
@Table(name="MainCat")
@SecondaryTables({ @SecondaryTable(name="Cat1", pkJoinColumns={ @PrimaryKeyJoinColumn(name="cat_id", referencedColumnName="id") ), @SecondaryTable(name="Cat2", uniqueConstraints={@UniqueConstraint(columnNames={"storyPart2"})}) })
public class Cat implements Serializable {

    private Integer id;
    private String name;
    private String storyPart1;
    private String storyPart2;

    @Id @GeneratedValue
    public Integer getId() {
        return id;
    }

    public String getName() {
        return name;
    }
    
    @Column(table="Cat1")
    public String getStoryPart1() {
        return storyPart1;
    }

    @Column(table="Cat2")
    public String getStoryPart2() {
        return storyPart2;
    }
In this example, name will be in MainCat. storyPart1 will be in Cat1 and storyPart2 will be in Cat2. Cat1 will be joined to MainCat using the cat_id as a foreign key, and Cat2 using id (ie the same column name, the MainCat id column has). Plus a unique constraint on storyPart2 has been set.
Check out the JBoss EJB 3 tutorial or the Hibernate Annotations unit test suite for more examples.

3.3. Mapping Queries

3.3.Mapping JPAQL/HQL queries. Mapping JPAQL/HQL queries

You can map EJBQL/HQL queries using annotations. @NamedQuery and @NamedQueries can be defined at the class level or in a JPA XML file. However their definitions are global to the session factory/entity manager factory scope. A named query is defined by its name and the actual query string.
<entity-mappings>
    <named-query name="plane.getAll">
        <query>select p from Plane p</query>
    </named-query>
    ...
</entity-mappings>
...

@Entity
@NamedQuery(name="night.moreRecentThan", query="select n from Night n where n.date >= :date")
public class Night {
    ...
}

public class MyDao {
    doStuff() {
        Query q = s.getNamedQuery("night.moreRecentThan");
        q.setDate( "date", aMonthAgo );
        List results = q.list();
        ...
    }
    ...
}
You can also provide some hints to a query through an array of QueryHint through a hints attribute.
The available Hibernate hints are

Table 3.2. Query hints

hint description
org.hibernate.cacheable Whether the query should interact with the second level cache (default to false)
org.hibernate.cacheRegion Cache region name (default used otherwise)
org.hibernate.timeout Query timeout
org.hibernate.fetchSize resultset fetch size
org.hibernate.flushMode Flush mode used for this query
org.hibernate.cacheMode Cache mode used for this query
org.hibernate.readOnly Entities loaded by this query should be in read only mode or not (default to false)
org.hibernate.comment Query comment added to the generated SQL

3.3.2. Mapping native queries

You can also map a native query (that is, a plain SQL query). To achieve that, you need to describe the SQL resultset structure using @SqlResultSetMapping (or @SqlResultSetMappings if you plan to define several resultset mappings). Like @NamedQuery, a @SqlResultSetMapping can be defined at class level or in a JPA XML file. However, its scope is global to the application.
As we will see, a resultSetMapping parameter is defined in @NamedNativeQuery, it represents the name of a defined @SqlResultSetMapping. The resultset mapping declares the entities retrieved by this native query. Each field of the entity is bound to an SQL alias (or column name). All fields of the entity including the ones of subclasses and the foreign key columns of related entities have to be present in the SQL query. Field definitions are optional provided that they map to the same column name as the one declared on the class property.
@NamedNativeQuery(name="night&area", query="select night.id nid, night.night_duration, "
    + " night.night_date, area.id aid, night.area_id, area.name "
    + "from Night night, Area area where night.area_id = area.id", resultSetMapping="joinMapping")
@SqlResultSetMapping(name="joinMapping", entities={
    @EntityResult(entityClass=org.hibernate.test.annotations.query.Night.class, fields = {
        @FieldResult(name="id", column="nid"),
        @FieldResult(name="duration", column="night_duration"),
        @FieldResult(name="date", column="night_date"),
        @FieldResult(name="area", column="area_id"),
        discriminatorColumn="disc"
    }),
    @EntityResult(entityClass=org.hibernate.test.annotations.query.Area.class, fields = {
        @FieldResult(name="id", column="aid"),
        @FieldResult(name="name", column="name")
    })
    }
)
In the above example, the night&area named query use the joinMapping result set mapping. This mapping returns 2 entities, Night and Area, each property is declared and associated to a column name, actually the column name retrieved by the query. Let's now see an implicit declaration of the property / column:
@Entity
@SqlResultSetMapping(name="implicit", entities=@EntityResult(entityClass=org.hibernate.test.annotations.query
.SpaceShip.class)) @NamedNativeQuery(name="implicitSample", query="select * from SpaceShip", resultSetMapping="implicit")
public class SpaceShip {
    private String name;
    private String model;
    private double speed;

    @Id
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Column(name="model_txt")
    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    public double getSpeed() {
        return speed;
    }

    public void setSpeed(double speed) {
        this.speed = speed;
    }
}
In this example, we only describe the entity member of the result set mapping. The property / column mapping is done using the entity mapping values. In this case the model property is bound to the model_txt column. If the association to a related entity involves a composite primary key, a @FieldResult element should be used for each foreign key column. The @FieldResult name is composed of the property name for the relationship, followed by a dot ("."), followed by the name or the field or property of the primary key.
@Entity
@SqlResultSetMapping(name="compositekey",
        entities=@EntityResult(entityClass=org.hibernate.test.annotations.query
        .SpaceShip.class,
            fields = {
                    @FieldResult(name="name", column = "name"),
                    @FieldResult(name="model", column = "model"),
                    @FieldResult(name="speed", column = "speed"),
                    @FieldResult(name="captain.firstname", column = "firstn"), @FieldResult(name="captain.lastname", column = "lastn"),
                    @FieldResult(name="dimensions.length", column = "length"),
                    @FieldResult(name="dimensions.width", column = "width")
                    }),
        columns = { @ColumnResult(name = "surface"),
                    @ColumnResult(name = "volume") } )

@NamedNativeQuery(name="compositekey",
    query="select name, model, speed, lname as lastn, fname as firstn, length, width, length * width as surface from SpaceShip", 
    resultSetMapping="compositekey")
} )
public class SpaceShip {
    private String name;
    private String model;
    private double speed;
    private Captain captain;
    private Dimensions dimensions;

    @Id
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @ManyToOne(fetch= FetchType.LAZY)
    @JoinColumns( {
            @JoinColumn(name="fname", referencedColumnName = "firstname"),
            @JoinColumn(name="lname", referencedColumnName = "lastname")
            } )
    public Captain getCaptain() {
        return captain;
    }

    public void setCaptain(Captain captain) {
        this.captain = captain;
    }

    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    public double getSpeed() {
        return speed;
    }

    public void setSpeed(double speed) {
        this.speed = speed;
    }

    public Dimensions getDimensions() {
        return dimensions;
    }

    public void setDimensions(Dimensions dimensions) {
        this.dimensions = dimensions;
    }
}

@Entity
@IdClass(Identity.class)
public class Captain implements Serializable {
    private String firstname;
    private String lastname;

    @Id
    public String getFirstname() {
        return firstname;
    }

    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }

    @Id
    public String getLastname() {
        return lastname;
    }

    public void setLastname(String lastname) {
        this.lastname = lastname;
    }
}

Note

If you look at the dimension property, you'll see that although EJB3 implementations do not have to support the dotted notation for embedded objects, Hobernate does. You can even have nested embedded objects.
If you retrieve a single entity and if you use the default mapping, you can use the resultClass attribute instead of resultSetMapping:
@NamedNativeQuery(name="implicitSample", query="select * from SpaceShip", resultClass=SpaceShip.class)
public class SpaceShip {
In some of your native queries, you'll have to return scalar values, for example when building report queries. You can map them in the @SqlResultsetMapping through @ColumnResult. You actually can even mix entities and scalar returns in the same native query (this is probably not common though).
@SqlResultSetMapping(name="scalar", columns=@ColumnResult(name="dimension")) @NamedNativeQuery(name="scalar", query="select length*width as dimension from SpaceShip", resultSetMapping="scalar")
Another query hint specific to native queries has been introduced: org.hibernate.callable which can be true or false depending on whether the query is a stored procedure or not.

3.4. Hibernate Annotation Extensions

Hibernate 3.1 offers a variety of additional annotations that you can mix/match with your EJB 3 entities. They have been designed as a natural extension of EJB3 annotations.
To empower the EJB3 capabilities, Hibernate provides specific annotations that match Hibernate features. The org.hibernate.annotations package contains all these annotations extensions.

3.4.1. Entity

You can fine tune some of the actions done by Hibernate on entities beyond what the EJB3 spec offers.
@org.hibernate.annotations.Entity adds additional metadata that may be needed beyond what is defined in the standard @Entity:
mutable
whether this entity is mutable or not
dynamicInsert
allow dynamic SQL for inserts
dynamicUpdate
allow dynamic SQL for updates
selectBeforeUpdate
Specifies that Hibernate should never perform an SQL UPDATE unless it is certain that an object is actually modified.
polymorphism
whether the entity polymorphism is of PolymorphismType.IMPLICIT (default) or PolymorphismType.EXPLICIT
optimisticLock
optimistic locking strategy (OptimisticLockType.VERSION, OptimisticLockType.NONE, OptimisticLockType.DIRTY or OptimisticLockType.ALL)

Note

@javax.persistence.Entity is still mandatory – @org.hibernate.annotations.Entity is not a replacement.
Here are some additional Hibernate annotation extensions:
@org.hibernate.annotations.BatchSize
allows you to define the batch size when fetching instances of this entity ( eg. @BatchSize(size=4) ). When loading a given entity, Hibernate will then load all the uninitialized entities of the same type in the persistence context up to the batch size.
@org.hibernate.annotations.Proxy
defines the laziness attributes of the entity. lazy (default to true) define whether the class is lazy or not. proxyClassName is the interface used to generate the proxy (default is the class itself).
@org.hibernate.annotations.Where
defines an optional SQL WHERE clause used when instances of this class is retrieved.
@org.hibernate.annotations.Check
defines an optional check constraints defined in the DDL statement.
@OnDelete(action=OnDeleteAction.CASCADE)
on joined subclasses: use a SQL cascade delete on deletion instead of the regular Hibernate mechanism.
@Table(appliesTo="tableName", indexes = { @Index(name="index1", columnNames={"column1", "column2"} ) } )
creates the defined indexes on the columns of table tableName. This can be applied on the primary table or any secondary table. The @Tables annotation allows your to apply indexes on different tables. This annotation is expected where @javax.persistence.Table or @javax.persistence.SecondaryTable(s) occurs.

Note

@org.hibernate.annotations.Table is a complement to, not a replacement for @javax.persistence.Table. In particular, if you want to change the default name of a table, you must use @javax.persistence.Table, not @org.hibernate.annotations.Table.
@org.hibernate.annotations.Table can also be used to define the following elements of secondary tables:
fetch
If set to JOIN, the default, Hibernate will use an inner join to retrieve a secondary table defined by a class or its superclasses and an outer join for a secondary table defined by a subclass. If set to select then Hibernate will use a sequential select for a secondary table defined on a subclass, which will be issued only if a row turns out to represent an instance of the subclass. Inner joins will still be used to retrieve a secondary defined by the class and its superclasses.
inverse
If true, Hibernate will not try to insert or update the properties defined by this join. Default to false.
optional
If enabled (the default), Hibernate will insert a row only if the properties defined by this join are non-null and will always use an outer join to retrieve the properties.
foreignKey
defines the Foreign Key name of a secondary table pointing back to the primary table.
@Immutable marks an entity as immutable. The entity may not be updated or deleted by the application. This allows Hibernate to make some minor performance optimizations. @Immutable must be use on root entities only.
@Persister lets you define your own custom persistence strategy. You may, for example, specify your own subclass of org.hibernate.persister.EntityPersister or you might even provide a completely new implementation of the interface org.hibernate.persister.ClassPersister that implements persistence via, for example, stored procedure calls, serialization to flat files or LDAP.
@Entity
@BatchSize(size=5)
@org.hibernate.annotations.Entity(
        selectBeforeUpdate = true,
        dynamicInsert = true, dynamicUpdate = true,
        optimisticLock = OptimisticLockType.ALL,
        polymorphism = PolymorphismType.EXPLICIT)
@Where(clause="1=1")
@org.hibernate.annotations.Table(appliesTo="Forest", indexes = { @Index(name="idx", columnNames = { "name", "length" } ) } )
@Persister(impl=MyEntityPersister.class)
public class Forest { ... }
@Entity
@Inheritance(
    strategy=InheritanceType.JOINED
)
public class Vegetable { ... }

@Entity
@OnDelete(action=OnDeleteAction.CASCADE)
public class Carrot extends Vegetable { ... }

3.4.Identifier. Identifier

Hibernate Annotations goes beyond the Java Persistence specification when defining identifiers.

3.4.Identifier.1. Generators

@org.hibernate.annotations.GenericGenerator and @org.hibernate.annotations.GenericGenerators allows you to define a Hibernate-specific id generator.
@Id @GeneratedValue(generator="system-uuid")
@GenericGenerator(name="system-uuid", strategy = "uuid")
public String getId() {

@Id @GeneratedValue(generator="hibseq")
@GenericGenerator(name="hibseq", strategy = "seqhilo",
    parameters = {
        @Parameter(name="max_lo", value = "5"),
        @Parameter(name="sequence", value="heybabyhey")
    }
)
public Integer getId() {
strategy is the short name of a Hibernate3 generator strategy or the fully qualified class name of an IdentifierGenerator implementation. You can add some parameters through the parameters attribute.
Contrary to their standard counterpart, @GenericGenerator and @GenericGenerators can be used in package-level annotations, making them application-level generators (just like if they were in a JPA XML file).
@GenericGenerators(
    {
    @GenericGenerator(
        name="hibseq",
        strategy = "seqhilo",
        parameters = {
            @Parameter(name="max_lo", value = "5"),
            @Parameter(name="sequence", value="heybabyhey")
        }
     ),
     @GenericGenerator(...)
     }
)
package org.hibernate.test.model

3.4.Identifier.2. @NaturalId

While not used as identifier property, some (groups of) properties represent the natural identifier of an entity. This is especially true when the schema uses the recommended approach of using surrogate primary key even if a natural business key exists. Hibernate allows to map such natural properties and reuse them in a Criteria query. The natural identifier is composed of all the properties marked @NaturalId.
@Entity
public class Citizen {
    @Id
    @GeneratedValue
    private Integer id;
    private String firstname;
    private String lastname;
    
    @NaturalId
    @ManyToOne
    private State state;

    @NaturalId
    private String ssn;
    ...
}



//and later on query
List results = s.createCriteria( Citizen.class )
                .add( Restrictions.naturalId().set( "ssn", "1234" ).set( "state", ste ) )
                .list();
Note that the group of properties representing the natural identifier have to be unique (Hibernate will generate a unique constraint if the database schema is generated).

3.4.3. Property

3.4.3.1. Access type

The access type is guessed from the position of @Id or @EmbeddedId in the entity hierarchy. Sub-entities, embedded objects and mapped superclass inherit the access type from the root entity.
In Hibernate, you can override the access type to:
  • use a custom access type strategy
  • fine tune the access type at the class level or at the property level
An @AccessType annotation has been introduced to support this behavior. You can define the access type on
  • an entity
  • a superclass
  • an embeddable object
  • a property
The access type is overridden for the annotated element, if overridden on a class, all the properties of the given class inherit the access type. For root entities, the access type is considered to be the default one for the whole hierarchy (overridable at class or property level).
If the access type is marked as "property", the getters are scanned for annotations, if the access type is marked as "field", the fields are scanned for annotations. Otherwise the elements marked with @Id or @embeddedId are scanned.
You can override an access type for a property, but the element to annotate will not be influenced: for example an entity having access type field, can annotate a field with @AccessType("property"), the access type will then be property for this attribute, the the annotations still have to be carried on the field.
If a superclass or an embeddable object is not annotated, the root entity access type is used (even if an access type has been define on an intermediate superclass or embeddable object). The "Matryoshka doll principle" does not apply.
@Entity
public class Person implements Serializable {
    @Id  @GeneratedValue //access type field
    Integer id;

    @Embedded
    @AttributeOverrides({
    @AttributeOverride(name = "iso2", column = @Column(name = "bornIso2")),
    @AttributeOverride(name = "name", column = @Column(name = "bornCountryName"))
            })
    Country bornIn;
}

@Embeddable
@AccessType("property") //override access type for all properties in Country
public class Country implements Serializable {
    private String iso2;
    private String name;

    public String getIso2() {
        return iso2;
    }

    public void setIso2(String iso2) {
        this.iso2 = iso2;
    }

    @Column(name = "countryName")
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

3.4.3.2. Formula

Sometimes, you want the Database to do some computation for you rather than in the JVM, you might also create some kind of virtual column. You can use a SQL fragment (aka formula) instead of mapping a property into a column. This kind of property is read only (its value is calculated by your formula fragment).
@Formula("obj_length * obj_height * obj_width")
public long getObjectVolume()
The SQL fragment can be as complex as you want and even include subselects.

3.4.3.3. Type

@org.hibernate.annotations.Type overrides the default Hibernate type used: this is generally not necessary since the type is correctly inferred by Hibernate. Please refer to the Hibernate Reference Guide for more information on the Hibernate types.
@org.hibernate.annotations.TypeDef and @org.hibernate.annotations.TypeDefs allows you to declare type definitions. These annotations are placed at the class or package level. Note that these definitions will be global for the session factory (even at the class level) and that type definition has to be defined before any usage.
@TypeDefs(
    {
    @TypeDef(
        name="caster",
        typeClass = CasterStringType.class,
        parameters = {
            @Parameter(name="cast", value="lower")
        }
    )
    }
)
package org.hibernate.test.annotations.entity;

...
public class Forest {
    @Type(type="caster")
    public String getSmallText() {
    ...
}
When using composite user type, you will have to express column definitions. The @Columns has been introduced for that purpose.
@Type(type="org.hibernate.test.annotations.entity.MonetaryAmountUserType")
@Columns(columns = {
    @Column(name="r_amount"),
    @Column(name="r_currency")
})
public MonetaryAmount getAmount() {
    return amount;
}


public class MonetaryAmount implements Serializable {
    private BigDecimal amount;
    private Currency currency;
    ...
}

3.4.3.4. Index

You can define an index on a particular column using the @Index annotation on a one column property, the columnNames attribute will then be ignored
@Column(secondaryTable="Cat1")
@Index(name="story1index")
public String getStoryPart1() {
    return storyPart1;
}

3.4.3.5. @Parent

When inside an embeddable object, you can define one of the properties as a pointer back to the owner element.
@Entity
public class Person {
    @Embeddable public Address address;
    ...
}

@Embeddable
public class Address {
    @Parent public Person owner;
    ...
}


person == person.address.owner

3.4.3.6. Generated properties

Some properties are generated at insert or update time by your database. Hibernate can deal with such properties and triggers a subsequent select to read these properties.
@Entity
public class Antenna {
    @Id public Integer id;
    @Generated(GenerationTime.ALWAYS) @Column(insertable = false, updatable = false)
    public String longitude;

    @Generated(GenerationTime.INSERT) @Column(insertable = false)
    public String latitude;
}
Annotate your property as @Generated. You have to make sure your insertability or updatability does not conflict with the generation strategy you have chosen. When GenerationTime.INSERT is chosen, the property must not contains insertable columns, when GenerationTime.ALWAYS is chosen, the property must not contains insertable nor updatable columns.
@Version properties cannot be @Generated(INSERT) by design, it has to be either NEVER or ALWAYS.

3.4.3.7. @Target

Sometimes, the type guessed by reflection is not the one you want Hibernate to use. This is especially true of components when an interface is used. You can use @Target to bypass the reflection guessing mechanism (very much like the targetEntity attribute available on associations.
@Embedded
    @Target(OwnerImpl.class)
    public Owner getOwner() {
        return owner;
    }

3.4.3.8. Optimistic lock

It is sometimes useful to avoid increasing the version number even if a given property is dirty (particularly collections). You can do that by annotating the property (or collection) with @OptimisticLock(excluded=true).
More formally, it specifies that updates to this property do not require acquisition of the optimistic lock.

3.4.4. Inheritance

SINGLE_TABLE is a very powerful strategy but sometimes, and especially for legacy systems, you cannot add an additional discriminator column. For that purpose, Hibernate has introduced the notion of discriminator formula: @DiscriminatorFormula is a replacement of @DiscriminatorColumn and use a SQL fragment as a formula for discriminator resolution (no need to have a dedicated column).
@Entity
@DiscriminatorFormula("case when forest_type is null then 0 else forest_type end")
public class Forest { ... }
By default, when querying the top entities, Hibernate does not put a restriction clause on the discriminator column. This can be inconvenient if this column contains values not mapped in your hierarchy (through @DiscriminatorValue). To work around that you can use @ForceDiscriminator (at the class level, next to @DiscriminatorColumn). Hibernate will then list the available values when loading the entities.
You can define the foreign key name generated by Hibernate for subclass tables in the JOINED inheritance strategy.
@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public abstract class File { ... }

@Entity
@ForeignKey(name = "FK_DOCU_FILE")
public class Document extends File {
The foreign key from the Document table to the File table will be named FK_DOCU_FILE.

3.4.5. Single Association related annotations

By default, when Hibernate cannot resolve the association because the expected associated element is not in database (wrong id on the association column), an exception is raised by Hibernate. This might be inconvenient for legacy and badly maintained schemas. You can ask Hibernate to ignore such elements instead of raising an exception using the @NotFound annotation. This annotation can be used on a @OneToOne (with FK), @ManyToOne, @OneToMany or @ManyToMany association.
@Entity
public class Child {
    ...
    @ManyToOne
    @NotFound(action=NotFoundAction.IGNORE)
    public Parent getParent() { ... }
    ...
}
Sometimes you want to delegate to your database the deletion of cascade when a given entity is deleted.
@Entity
public class Child {
    ...
    @ManyToOne
    @OnDelete(action=OnDeleteAction.CASCADE)
    public Parent getParent() { ... }
    ...
}
In this case Hibernate generates a cascade delete constraint at the database level.
Foreign key constraints, when generated by Hibernate, have a fairly unreadable name. You can override the constraint name by using @ForeignKey.
@Entity
public class Child {
    ...
    @ManyToOne
    @ForeignKey(name="FK_PARENT")
    public Parent getParent() { ... }
    ...
}

alter table Child add constraint FK_PARENT foreign key (parent_id) references Parent

3.4.5.1. Lazy options and fetching modes

EJB3 comes with the fetch option to define lazy loading and fetching modes, however Hibernate has a much greater option set in this area. To fine tune the lazy loading and fetching strategies, some additional annotations have been introduced:
@LazyToOne
defines the lazyness option on @ManyToOne and @OneToOne associations. LazyToOneOption can be PROXY (ie use a proxy based lazy loading), NO_PROXY (use a bytecode enhancement based lazy loading - note that build time bytecode processing is necessary) and FALSE (association not lazy)
@LazyCollection>
defines the lazyness option on @ManyToMany and @OneToMany associations. LazyCollectionOption can be TRUE (the collection is lazy and will be loaded when its state is accessed), EXTRA (the collection is lazy and all operations will try to avoid the collection loading, this is especially useful for huge collections when loading all the elements is not necessary) and FALSE (association not lazy)
@Fetch>
defines the fetching strategy used to load the association. FetchMode can be SELECT (a select is triggered when the association needs to be loaded), SUBSELECT (only available for collections, use a subselect strategy - please refer to the Hibernate Reference Documentation for more information) or JOIN (use a SQL JOIN to load the association while loading the owner entity). JOIN overrides any lazy attribute (an association loaded through a JOIN strategy cannot be lazy).
The Hibernate annotations override the EJB3 fetching options.

Table 3.3. Lazy and fetch options equivalent

Annotations Lazy Fetch
@[One|Many]ToOne](fetch=FetchType.LAZY) @LazyToOne(PROXY) @Fetch(SELECT)
@[One|Many]ToOne](fetch=FetchType.EAGER) @LazyToOne(FALSE) @Fetch(JOIN)
@ManyTo[One|Many](fetch=FetchType.LAZY) @LazyCollection(TRUE) @Fetch(SELECT)
@ManyTo[One|Many](fetch=FetchType.EAGER) @LazyCollection(FALSE) @Fetch(JOIN)

3.4.5.2. @Any

The @Any annotation defines a polymorphic association to classes from multiple tables. This type of mapping always requires more than one column. The first column holds the type of the associated entity. The remaining columns hold the identifier. It is impossible to specify a foreign key constraint for this kind of association, so this is most certainly not meant as the usual way of mapping (polymorphic) associations. You should use this only in very special cases (eg. audit logs, user session data, etc).
The @Any annotation describes the column holding the metadata information. To link the value of the metadata information and an actual entity type, The @AnyDef and @AnyDefs annotations are used.
@Any( metaColumn = @Column( name = "property_type" ), fetch=FetchType.EAGER )
    @AnyMetaDef( 
        idType = "integer", 
        metaType = "string", 
        metaValues = {
            @MetaValue( value = "S", targetEntity = StringProperty.class ),
            @MetaValue( value = "I", targetEntity = IntegerProperty.class )
        } )
    @JoinColumn( name = "property_id" )
    public Property getMainProperty() {
        return mainProperty;
    }
idType represents the target entities identifier property type and metaType the metadata type (usually String).
Note that @AnyDef can be mutualized and reused. It is recommended to place it as a package metadata in this case.
//on a package
@AnyMetaDef( name="property" 
    idType = "integer", 
    metaType = "string", 
    metaValues = {
        @MetaValue( value = "S", targetEntity = StringProperty.class ),
        @MetaValue( value = "I", targetEntity = IntegerProperty.class )
    } )
package org.hibernate.test.annotations.any;


//in a class
    @Any( metaDef="property", metaColumn = @Column( name = "property_type" ), fetch=FetchType.EAGER )
    @JoinColumn( name = "property_id" )
    public Property getMainProperty() {
        return mainProperty;
    }

3.4.6. Collection related annotations

3.4.6.1. Enhance collection settings

It is possible to set
  • the batch size for collections using @BatchSize
  • the where clause, using @Where (applied on the target entity) or @WhereJoinTable (applied on the association table)
  • the check clause, using @Check
  • the SQL order by clause, using @OrderBy
  • the delete cascade strategy through @OnDelete(action=OnDeleteAction.CASCADE)
  • the collection immutability using @Immutable: if set specifies that the elements of the collection never change (a minor performance optimization in some cases)
  • a custom collection persister (ie the persistence strategy used) using @Persister: the class must implement org.hibernate.persister.collectionCollectionPersister
You can also declare a sort comparator. Use the @Sort annotation. Expressing the comparator type you want between unsorted, natural or custom comparator. If you want to use your own comparator implementation, you'll also have to express the implementation class using the comparator attribute. Note that you need to use either a SortedSet or a SortedMap interface.
@OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER)
    @JoinColumn(name="CUST_ID")
    @Sort(type = SortType.COMPARATOR, comparator = TicketComparator.class)
    @Where(clause="1=1")
    @OnDelete(action=OnDeleteAction.CASCADE)
    public SortedSet<Ticket> getTickets() {
        return tickets;
    }
Please refer to the previous descriptions of these annotations for more information.
Foreign key constraints, while generated by Hibernate, have a fairly unreadable name. You can override the constraint name by use @ForeignKey. Note that this annotation has to be placed on the owning side of the relationship, inverseName referencing to the other side constraint.
@Entity
public class Woman {
    ...
    @ManyToMany(cascade = {CascadeType.ALL})
    @ForeignKey(name = "TO_WOMAN_FK", inverseName = "TO_MAN_FK")
    public Set<Man> getMens() {
        return mens;
    }
}

alter table Man_Woman add constraint TO_WOMAN_FK foreign key (woman_id) references Woman
alter table Man_Woman add constraint TO_MAN_FK foreign key (man_id) references Man

3.4.6.2. Extra collection types

3.4.6.2.1. List
Beyond EJB3, Hibernate Annotations supports true List and Array. Map your collection the same way as usual and add the @IndexColumn. This annotation allows you to describe the column that will hold the index. You can also declare the index value in DB that represent the first element (aka as base index). The usual value is 0 or 1.
@OneToMany(cascade = CascadeType.ALL)
@IndexColumn(name = "drawer_position", base=1)
public List<Drawer> getDrawers() {
    return drawers;
}

Note

If you forgot to set @IndexColumn, the bag semantic is applied. If you want the bag semantic without the limitations of it, consider using @CollectionId.
3.4.6.2.2. Map
Hibernate Annotations also supports true Map mappings. If @javax.persistence.MapKey is not set, Hibernate will map the key element or embeddable object in its/their own columns. To overrides the default columns, you can use @org.hibernate.annotations.MapKey if your key is a basic type (defaulted to mapkey) or an embeddable object, or you can use @org.hibernate.annotations.MapKeyManyToMany if your key is an entity.
Both @org.hibernate.annotations.MapKey and @org.hibernate.annotations.MapKeyManyToMany allow you to override the target element to be used. This is especially useful if your collection does not use generics (or if you use interfaces).
@CollectionOfElements(targetElement = SizeImpl.class)
    @MapKeyManyToMany(targetEntity = LuggageImpl.class)
    private Map<Luggage, Size> sizePerLuggage = new HashMap<Luggage, Size>();
3.4.6.2.3. Bidirectional association with indexed collections
A bidirectional association where one end is an indexed collection (that is, represented as a @IndexColumn, @org.hibernate.annotations.MapKey or @org.hibernate.annotations.MapKeyManyToMany) requires special consideration. If a property on the associated class explicitly maps the indexed value, the use of mappedBy is permitted:
@Entity
public class Parent {
    @OneToMany(mappedBy="parent")
    @org.hibernate.annotations.IndexColumn(name="order")
    private List<Child> children;
    ...
}

@Entity
public class Child {
    ...
    //the index column is mapped as a property in the associated entity
    @Column(name="order")
    private int order;

    @ManyToOne
    @JoinColumn(name="parent_id", nullable=false)
    private Parent parent;
    ...
}
But, if there is no such property on the child class, we can't think of the association as truly bidirectional (there is information available at one end of the association that is not available at the other end: the index). In this case, we can't map the collection as mappedBy. Instead, we could use the following mapping:
@Entity
public class Parent {
    @OneToMany
    @org.hibernate.annotations.IndexColumn(name="order")
    @JoinColumn(name="parent_id", nullable=false)
    private List<Child> children;
    ...
}

@Entity
public class Child {
    ...
    @ManyToOne
    @JoinColumn(name="parent_id", insertable=false, updatable=false, nullable=false)
    private Parent parent;
    ...
}
Note that in this mapping, the collection-valued end of the association is responsible for updating the foreign key.
3.4.6.2.4. Bag with primary key
Another interesting feature is the ability to define a surrogate primary key to a bag collection. This removes pretty much all of the drawbacks of bags: update and removal are efficient, more than one EAGER bag per query or per entity. This primary key will be contained in an additional column of your collection table but will not be visible to the Java application. @CollectionId is used to mark a collection as id bag, it also allow to override the primary key column(s), the primary key type and the generator strategy. The strategy can be identity, or any defined generator name of your application.
@Entity
@TableGenerator(name="ids_generator", table="IDS")
public class Passport {
    ...

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name="PASSPORT_VISASTAMP")
    @CollectionId( columns = @Column(name="COLLECTION_ID"), type=@Type(type="long"), generator = "ids_generator" )
    private Collection<Stamp> visaStamp = new ArrayList();
    ...
}
3.4.6.2.5. Collection of element or composite elements
Hibernate Annotations also supports collections of core types (Integer, String, Enums, ...), collections of embeddable objects and even arrays of primitive types. This is known as collection of elements.
A collection of elements has to be annotated as @CollectionOfElements (as a replacement of @OneToMany) To define the collection table, the @JoinTable annotation is used on the association property, joinColumns defines the join columns between the entity primary table and the collection table (inverseJoincolumn is useless and should be left empty). For collection of core types or array of primitive types, you can override the element column definition using a @Column on the association property. You can also override the columns of a collection of embeddable object using @AttributeOverride. To reach the collection element, you need to append "element" to the attribute override name (eg "element" for core types, or "element.serial" for the serial property of an embeddable element). To reach the index/key of a collection, append "key" instead.
@Entity
public class Boy {
    private Integer id;
    private Set<String> nickNames = new HashSet<String>();
    private int[] favoriteNumbers;
    private Set<Toy> favoriteToys = new HashSet<Toy>();
    private Set<Character> characters = new HashSet<Character>();

    @Id @GeneratedValue
    public Integer getId() {
        return id;
    }

    @CollectionOfElements public Set<String> getNickNames() {
        return nickNames;
    }

    @CollectionOfElements @JoinTable( name="BoyFavoriteNumbers", joinColumns = @JoinColumn(name="BoyId") ) @Column(name="favoriteNumber", nullable=false)
    @IndexColumn(name="nbr_index")
    public int[] getFavoriteNumbers() {
        return favoriteNumbers;
    }

    @CollectionOfElements @AttributeOverride( name="element.serial", column=@Column(name="serial_nbr") )
    public Set<Toy> getFavoriteToys() {
        return favoriteToys;
    }

    @CollectionOfElements public Set<Character> getCharacters() {
        return characters;
    }
    ...
}

public enum Character {
    GENTLE,
    NORMAL,
    AGGRESSIVE,
    ATTENTIVE,
    VIOLENT,
    CRAFTY
}

@Embeddable
public class Toy {
    public String name;
    public String serial;
    public Boy owner;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSerial() {
        return serial;
    }

    public void setSerial(String serial) {
        this.serial = serial;
    }

    @Parent
    public Boy getOwner() {
        return owner;
    }

    public void setOwner(Boy owner) {
        this.owner = owner;
    }

    public boolean equals(Object o) {
        if ( this == o ) return true;
        if ( o == null || getClass() != o.getClass() ) return false;

        final Toy toy = (Toy) o;

        if ( !name.equals( toy.name ) ) return false;
        if ( !serial.equals( toy.serial ) ) return false;

        return true;
    }

    public int hashCode() {
        int result;
        result = name.hashCode();
        result = 29 * result + serial.hashCode();
        return result;
    }
}
On a collection of embeddable objects, the embeddable object can have a property annotated with @Parent. This property will then point back to the entity containing the collection.

Note

Previous versions of Hibernate Annotations used the @OneToMany to mark a collection of elements. Due to semantic inconsistencies, we've introduced the annotation @CollectionOfElements. Marking collections of elements the old way still work but is considered deprecated and is going to be unsupported in future releases
3.4.6.2.6. @ManyToAny
@ManyToAny allows polymorphic associations to classes from multiple tables. This type of mapping always requires more than one column. The first column holds the type of the associated entity. The remaining columns hold the identifier. It is impossible to specify a foreign key constraint for this kind of association, so this is most certainly not meant as the usual way of mapping (polymorphic) associations. You should use this only in very special cases (eg. audit logs, user session data, etc).
@ManyToAny(
            metaColumn = @Column( name = "property_type" ) )
    @AnyMetaDef( 
        idType = "integer", 
        metaType = "string",
        metaValues = {
            @MetaValue( value = "S", targetEntity = StringProperty.class ),
            @MetaValue( value = "I", targetEntity = IntegerProperty.class ) } )
    @Cascade( { org.hibernate.annotations.CascadeType.ALL } )
    @JoinTable( name = "obj_properties", joinColumns = @JoinColumn( name = "obj_id" ),
            inverseJoinColumns = @JoinColumn( name = "property_id" ) )
    public List<Property> getGeneralProperties() {
Like @Any, @ManyToAny can use named @AnyDefs, see Section 3.4.5.2, “@Any” for more information.

3.4.7. Cascade

Hibernate offers more operations than the Java Persistence specification. You can use the @Cascade annotation to cascade the following operations:
  • PERSIST
  • MERGE
  • REMOVE
  • REFRESH
  • DELETE
  • SAVE_UPDATE
  • REPLICATE
  • DELETE_ORPHAN
  • LOCK
  • EVICT
This is especially useful for SAVE_UPDATE (which is the operation cascaded at flush time if you use plain Hibernate Annotations - Hibernate EntityManager cascade PERSIST at flush time as per the specification). DELETE_ORPHAN applies only to @OneToMany associations, and indicates that the delete()/remove() operation should be applied to any child object that is removed from the association. In other words, if a child is dereferenced by a persistent parent and if DELETE_ORPHAN is used, the "orphaned" child is deleted.
@OneToMany( cascade = {CascadeType.PERSIST, CascadeType.MERGE} ) @Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE, org.hibernate.annotations.CascadeType.DELETE_ORPHAN})
public Collection<Employer> getEmployers()
It is recommended to use @Cascade to compliment @*To*(cascade=...) as shown in the previous example.

3.4.8. Cache

In order to optimize your database accesses, you can activate the so-called second level cache of Hibernate. This cache is configurable on a per-entity and per-collection basis.
@org.hibernate.annotations.Cache defines the caching strategy and region of a given second level cache. This annotation can be applied on the root entity (not the sub entities), and on the collections.
@Entity
@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
public class Forest { ... }
@OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER)
    @JoinColumn(name="CUST_ID")
    @Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
    public SortedSet<Ticket> getTickets() {
        return tickets;
    }
@Cache(
    CacheConcurrencyStrategy usage();
    String region() default "";
    String include() default "all";
)

Notes:

  1. usage: the given cache concurrency strategy (NONE, READ_ONLY, NONSTRICT_READ_WRITE, READ_WRITE, TRANSACTIONAL)
  2. region (optional): the cache region (default to the fqcn of the class or the fq role name of the collection)
  3. include (optional): all to include all properties, non-lazy to only include non lazy properties (default all).

3.4.9. Filters

Hibernate has the ability to apply arbitrary filters on top of your data. Those filters are applied at runtime on a given session. First, you need to define them.
@org.hibernate.annotations.FilterDef or @FilterDefs define filter definition(s) used by filter(s) using the same name. A filter definition has a name() and an array of parameters(). A parameter will allow you to adjust the behavior of the filter at runtime. Each parameter is defined by a @ParamDef which has a name and a type. You can also define a defaultCondition() parameter for a given @FilterDef to set the default condition to use when none are defined in each individual @Filter. A @FilterDef(s) can be defined at the class or package level.
We now need to define the SQL filter clause applied to either the entity load or the collection load. @Filter is used and placed either on the entity or the collection element
@Entity
@FilterDef(name="minLength", parameters=@ParamDef( name="minLength", type="integer" ) )
@Filters( {
    @Filter(name="betweenLength", condition=":minLength <= length and :maxLength >= length"),
    @Filter(name="minLength", condition=":minLength <= length")
} )
public class Forest { ... }
When the collection uses an association table as a relational representation, you might want to apply the filter condition to the association table itself or to the target entity table. To apply the constraint on the target entity, use the regular @Filter annotation. However, if you want to target the association table, use the @FilterJoinTable annotation.
@OneToMany
    @JoinTable
    //filter on the target entity table
    @Filter(name="betweenLength", condition=":minLength <= length and :maxLength >= length")
    //filter on the association table
    @FilterJoinTable(name="security", condition=":userlevel >= requredLevel")
    public Set<Forest> getForests() { ... }

3.4.10. Queries

Since Hibernate has more features on named queries than the one defined in the EJB3 specification, @org.hibernate.annotations.NamedQuery, @org.hibernate.annotations.NamedQueries, @org.hibernate.annotations.NamedNativeQuery and @org.hibernate.annotations.NamedNativeQueries have been introduced. They add attributes to the standard version and can be used as a replacement:
flushMode
defines the query flush mode (Always, Auto, Commit or Manual)
cacheable
whether the query should be cached or not
cacheRegion
cache region used if the query is cached
fetchSize
JDBC statement fetch size for this query
timeout
query time out
callable
for native queries only, to be set to true for stored procedures
comment
if comments are activated, the comment seen when the query is sent to the database.
cacheMode
Cache interaction mode (get, ignore, normal, put or refresh)
readOnly
whether or not the elements retrievent from the query are in read-only mode.
Those hints can be set in a standard @javax.persistence.NamedQuery annotations through the detyped @QueryHint. Another key advantage is the ability to set those annotations at a package level.

3.4.11. Custom SQL for CRUD operations

Hibernate gives you the ability to override every single SQL statement generated. We have seen native SQL query usage already, but you can also override the SQL statement used to load or change the state of entities.
@Entity
@Table(name="CHAOS")
@SQLInsert( sql="INSERT INTO CHAOS(size, name, nickname, id) VALUES(?,upper(?),?,?)") @SQLUpdate( sql="UPDATE CHAOS SET size = ?, name = upper(?), nickname = ? WHERE id = ?") @SQLDelete( sql="DELETE CHAOS WHERE id = ?") @SQLDeleteAll( sql="DELETE CHAOS") @Loader(namedQuery = "chaos")
@NamedNativeQuery(name="chaos", query="select id, size, name, lower( nickname ) as nickname from CHAOS where id= ?", resultClass = Chaos.class)
public class Chaos {
    @Id
    private Long id;
    private Long size;
    private String name;
    private String nickname;
@SQLInsert, @SQLUpdate, @SQLDelete, @SQLDeleteAll respectively override the INSERT statement, UPDATE statement, DELETE statement, DELETE statement to remove all entities.
If you expect to call a store procedure, be sure to set the callable attribute to true (@SQLInsert(callable=true, ...)).
To check that the execution happens correctly, Hibernate allows you to define one of those three strategies:
NONE
no check is performed: the store procedure is expected to fail upon issues
COUNT
use of rowcount to check that the update is successful
PARAM
like COUNT but using an output parameter rather that the standard mechanism
To define the result check style, use the check parameter (@SQLUpdate(check=ResultCheckStyle.COUNT, ...)).
You can also override the SQL load statement by a native SQL query or a HQL query. You just have to refer to a named query with the @Loader annotation.
You can use the exact same set of annotations to override the collection related statements.
@OneToMany
@JoinColumn(name="chaos_fk")
@SQLInsert( sql="UPDATE CASIMIR_PARTICULE SET chaos_fk = ? where id = ?") @SQLDelete( sql="UPDATE CASIMIR_PARTICULE SET chaos_fk = null where id = ?")
private Set<CasimirParticle> particles = new HashSet<CasimirParticle>();
The order of the parameters is important and is defined by the order Hibernate handles properties. You can see the expected order by enabling debug logging for the org.hibernate.persister.entity level. With this, level-enabled Hibernate will print out the static SQL that is used to create, update, delete etc. entities. (To see the expected sequence, remember not to include your custom SQL through annotations as that will override the Hibernate-generated static sql.)
Overriding SQL statements for secondary tables is also possible using @org.hibernate.annotations.Table and either (or all) attributes sqlInsert, sqlUpdate, sqlDelete:
@Entity
@SecondaryTables({
    @SecondaryTable(name = "`Cat nbr1`"),
    @SecondaryTable(name = "Cat2"})
@org.hibernate.annotations.Tables( {
    @Table(appliesTo = "Cat", comment = "My cat table" ),
    @Table(appliesTo = "Cat2", foreignKey = @ForeignKey(name="FK_CAT2_CAT"), fetch = FetchMode.SELECT,
        sqlInsert=@SQLInsert(sql="insert into Cat2(storyPart2, id) values(upper(?), ?)") )
} )
public class Cat implements Serializable {
The previous example also show that you can give a comment to a given table (primary or secondary): This comment will be used for DDL generation.

3.4.12. Tuplizer

org.hibernate.tuple.Tuplizer, and its sub-interfaces, are responsible for managing a particular representation of a piece of data, given that representation's org.hibernate.EntityMode. If a given piece of data is thought of as a data structure, then a tuplizer is the thing which knows how to create such a data structure and how to extract values from and inject values into such a data structure. For example, for the POJO entity mode, the corresponding tuplizer knows how create the POJO through its constructor and how to access the POJO properties using the defined property accessors. There are two high-level types of Tuplizers, represented by the org.hibernate.tuple.EntityTuplizer and org.hibernate.tuple.ComponentTuplizer interfaces. EntityTuplizers are responsible for managing the above mentioned contracts in regards to entities, while ComponentTuplizers do the same for components. Check the Hibernate Reference Documentation for more information.
To define tuplixer in annotations, simply use the @Tuplizer annotation on the according element
@Entity
@Tuplizer(impl = DynamicEntityTuplizer.class)
public interface Cuisine {
    @Id
    @GeneratedValue
    public Long getId();
    public void setId(Long id);

    public String getName();
    public void setName(String name);

    @Tuplizer(impl = DynamicComponentTuplizer.class)
    public Country getCountry();
    public void setCountry(Country country);


}

Chapter 4. Overriding metadata through XML

The primary target for metadata in EJB3 is annotations, but the EJB3 specification provides a way to override or replace the annotation-defined metadata through an XML deployment descriptor. In the current release only pure EJB3 annotations overriding are supported. If you wish to use Hibernate-specific features in some entities, you'll have to either use annotations or fallback to hbm files. You can of course mix and match annotated entities and entities described in hbm files.
The unit test suite shows some additional XML file samples.

4.1. Principles

The XML deployment descriptor structure has been designed to reflect the annotations one. So if you know the annotations structure, using the XML schema will be straightforward for you.
You can define one or more XML files describing your metadata, these files will be merged by the overriding engine.

4.1.1. Global level metadata

You can define global level metadata available for all XML files. You must not define these metadata more than once per deployment.
<?xml version="1.0" encoding="UTF-8"?>

<entity-mappings 
  xmlns="http://java.sun.com/xml/ns/persistence/orm"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm orm_1_0.xsd"
  version="1.0">

    <persistence-unit-metadata>
        <xml-mapping-metadata-complete/>
        <persistence-unit-defaults>
            <schema>myschema</schema>
            <catalog>mycatalog</catalog>
            <cascade-persist/>
        </persistence-unit-defaults>
    </persistence-unit-metadata>
xml-mapping-metadata-complete means that all entity, mapped-superclasses and embeddable metadata should be picked up from XML (that is, ignore annotations).
schema / catalog will override all default definitions of schema and catalog in the metadata (both XML and annotations).
cascade-persist means that all associations have PERSIST as a cascade type. We recommend you to not use this feature.

4.1.2. Entity level metadata

You can either define or override metadata information on a given entity.
<?xml version="1.0" encoding="UTF-8"?>

<entity-mappings 
  xmlns="http://java.sun.com/xml/ns/persistence/orm"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm orm_1_0.xsd"
  version="1.0">

    <package>org.hibernate.test.annotations.reflection</package>
    <entity class="Administration" access="PROPERTY" metadata-complete="true">
        <table name="tbl_admin">
            <unique-constraint>
                <column-name>firstname</column-name>
                <column-name>lastname</column-name>
            </unique-constraint>
        </table>
        <secondary-table name="admin2">
            <primary-key-join-column name="admin_id" referenced-column-name="id"/>
            <unique-constraint>
                <column-name>address</column-name>
            </unique-constraint>
        </secondary-table>
        <id-class class="SocialSecurityNumber"/>
        <inheritance strategy="JOINED"/>
        <sequence-generator name="seqhilo" sequence-name="seqhilo"/>
        <table-generator name="table" table="tablehilo"/>
        ...
    </entity>

    <entity class="PostalAdministration">
        <primary-key-join-column name="id"/>
        ...
    </entity>
</entity-mappings>

Notes

  1. entity-mappings: entity-mappings is the root element for all XML files. You must declare the xml schema, the schema file is included in the hibernate-annotations.jar file, no Internet access will be processed by Hibernate Annotations.
  2. package (optional): default package used for all non qualified class names in the given deployment descriptor file.
  3. entity: describes an entity.
    metadata-complete defines whether the metadata description for this element is complete or not (in other words, if annotations present at the class level should be considered or not).
    An entity has to have a class attribute referring to the java class the metadata applies on.
    You can overrides entity name through the name attribute, if none is defined and if an @Entity.name is present, then it is used (provided that metadata complete is not set).
    For metadata complete (see below) element, you can define an access (either FIELD or PROPERTY (default)). For non metadata complete element, if access is not defined, the @Id position will lead position, if access is defined, the value is used.
  4. table: you can declare table properties (name, schema, catalog), if none is defined, the java annotation is used.
    You can define one or several unique constraints as seen in the example
  5. secondary-table: defines a secondary table very much like a regular table except that you can define the primary key / foreign key column(s) through the primary-key-join-column element. On non metadata complete, annotation secondary tables are used only if there is no secondary-table definition, annotations are ignored otherwise.
  6. id-class: defines the id class in a similar way @IdClass does
  7. inheritance: defines the inheritance strategy (JOINED, TABLE_PER_CLASS, SINGLE_TABLE), Available only at the root entity level
  8. sequence-generator: defines a sequence generator
  9. table-generator: defines a table generator
  10. primary-key-join-column: defines the primary key join column for sub entities when JOINED inheritance strategy is used
<?xml version="1.0" encoding="UTF-8"?>

<entity-mappings 
  xmlns="http://java.sun.com/xml/ns/persistence/orm"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm orm_1_0.xsd"
  version="1.0">

    <package>org.hibernate.test.annotations.reflection</package>
    <entity class="Music" access="PROPERTY" metadata-complete="true">
        <discriminator-value>Generic</discriminator-value>
        <discriminator-column length="34"/>
        ...
    </entity>

    <entity class="PostalAdministration">
        <primary-key-join-column name="id"/>
        <named-query name="adminById">
            <query>select m from Administration m where m.id = :id</query>
            <hint name="org.hibernate.timeout" value="200"/>
        </named-query>
        <named-native-query name="allAdmin" result-set-mapping="adminrs">
            <query>select *, count(taxpayer_id) as taxPayerNumber 
            from Administration, TaxPayer
            where taxpayer_admin_id = admin_id group by ...</query>
            <hint name="org.hibernate.timeout" value="200"/>
        </named-native-query>
        <sql-result-set-mapping name="adminrs">
            <entity-result entity-class="Administration">
                <field-result name="name" column="fld_name"/>
            </entity-result>
            <column-result name="taxPayerNumber"/>
        </sql-result-set-mapping>
        <attribute-override name="ground">
            <column name="fld_ground" unique="true" scale="2"/>
        </attribute-override>
        <association-override name="referer">
            <join-column name="referer_id" referenced-column-name="id"/>
        </association-override>
        ...
    </entity>
</entity-mappings>

Notes

  1. discriminator-value / discriminator-column: defines the discriminator value and the column holding it when the SINGLE_TABLE inheritance strategy is chosen
  2. named-query: defines named queries and possibly the hints associated to them. Those definitions are additive to the one defined in annotations, if two definitions have the same name, the XML one has priority.
  3. named-native-query: defines an named native query and its sql result set mapping. Alternatively, you can define the result-class. Those definitions are additive to the one defined in annotations, if two definitions have the same name, the XML one has priority.
  4. sql-result-set-mapping: describes the result set mapping structure. You can define both entity and column mappings. Those definitions are additive to the one defined in annotations, if two definitions have the same name, the XML one has priority
  5. attribute-override / association-override: defines a column or join column overriding. This overriding is additive to the one defined in annotations
Same applies for <embeddable> and <mapped-superclass>.

4.1.3. Property level metadata

You can of course define XML overriding for properties. If metadata complete is defined, then additional properties (ie at the Java level) will be ignored. Otherwise, once you start overriding a property, all annotations on the given property are ignored. All property level metadata resides in entity/attributes, mapped-superclass/attributes or embeddable/attributes.
<attributes>
        <id name="id">
            <column name="fld_id"/>
            <generated-value generator="generator" strategy="SEQUENCE"/>
            <temporal>DATE</temporal>
            <sequence-generator name="generator" sequence-name="seq"/>
        </id>
        <version name="version"/>
        <embedded name="embeddedObject">
            <attribute-override name"subproperty">
                <column name="my_column"/>
            </attribute-override>
        </embedded>
        <basic name="status" optional="false">
            <enumerated>STRING</enumerated>
        </basic>
        <basic name="serial" optional="true">
            <column name="serialbytes"/>
            <lob/>
        </basic>
        <basic name="terminusTime" fetch="LAZY">
            <temporal>TIMESTAMP</temporal>
        </basic>
    </attributes>
You can override a property through id, embedded-id, version, embedded and basic. Each of these elements can have sub-elements accordingly: lob, temporal, enumerated, column.

4.1.4. Association level metadata

You can define XML overriding for associations. All association level metadata behave in entity/attributes, mapped-superclass/attributes or embeddable/attributes.
<attributes>
        <one-to-many name="players" fetch="EAGER">
            <map-key name="name"/>
            <join-column name="driver"/>
            <join-column name="number"/>
        </one-to-many>
        <many-to-many name="roads" target-entity="Administration">
            <order-by>maxSpeed</order-by>
            <join-table name="bus_road">
                <join-column name="driver"/>
                <join-column name="number"/>
                <inverse-join-column name="road_id"/>
                <unique-constraint>
                    <column-name>driver</column-name>
                    <column-name>number</column-name>
                </unique-constraint>
            </join-table>
        </many-to-many>
        <many-to-many name="allTimeDrivers" mapped-by="drivenBuses">
    </attributes>
You can override an association through one-to-many, one-to-one, many-to-one, and many-to-many. Each of these elements can have sub-elements accordingly: join-table (which can have join-columns and inverse-join-columns), join-columns, map-key, and order-by. mapped-by and target-entity can be defined as attributes when it makes sense. Once again the structure is reflects the annotations structure. You can find all semantic information in Chapter 3, Entity Beans.

Chapter 5. Additional modules

Hibernate Annotations mainly focuses on persistence metadata. The project also has a nice integration with two Hibernate modules.

5.1. Hibernate Validator

5.1.1. Description

Annotations are a very convenient and elegant way to specify invariant constraints for a domain model. You can, for example, express that a property should never be null, that the account balance should be strictly positive, etc. These domain-model constraints are declared in the bean itself by annotating its properties. A validator can then read them and check for constraint violations. The validation mechanism can be executed in different layers in your application without having to duplicate any of these rules (presentation layer, data access layer). Following the DRY principle, Hibernate Validator has been designed for that purpose.
Hibernate Validator works at two levels. First, it is able to check in-memory instances of a class for constraint violations. Second, it can apply the constraints to the Hibernate meta-model and incorporate them into the generated database schema.
Each constraint annotation is associated to a validator implementation responsible for checking the constraint on the entity instance. A validator can also (optionally) apply the constraint to the Hibernate meta-model, allowing Hibernate to generate DDL that expresses the constraint. With the appropriate event listener, you can execute the checking operation on inserts and updates done by Hibernate. Hibernate Validator is not limited to use with Hibernate. You can easily use it anywhere in your application.
When checking instances at runtime, Hibernate Validator returns information about constraint violations in an array of InvalidValue s. Among other information, the InvalidValue contains an error description message that can embed the parameter values bundle with the annotation (eg. length limit), and message strings that may be externalized to a ResourceBundle .

5.1.2. Integration with Hibernate Annotations

If Hibernate Validator (hibernate-validator.jar) is available in the classpath, Hibernate Annotations will integrate it in two ways:
  • Constraints will be applied to the Data Definition Language. In other words, the database schema will reflect the constraints (provided that you use the hbm2ddl tool).
  • Before an entity change is applied to the database (insert or update), the entity is validated. Validation errors, if any, will be carried over through an InvalidStateException.
For entities free of validation rules, the runtime performance cost is null.
To disable constraint propagation to DDL, set up hibernate.validator.apply_to_ddl to false in the configuration file. Such a need is very uncommon and not recommended.
To disable pre-entity change validation, set up hibernate.validator.autoregister_listeners to false in the configuration file. Such a need is very uncommon and not recommended.
Check the Hibernate Validator reference documentation for more information.

5.2. Hibernate Search

5.2.1. Description

Full-text search engines like Apache Lucene are a very powerful technology to bring free text/efficient queries to applications. Ift suffers several mismatches when dealing with a object domain model (keeping the index up-to-date, mismatch between the index structure and the domain model, querying mismatch...) Hibernate Search indexes your domain model thanks to a few annotations, takes care of the database / index synchronization and brings you back regular managed objects from free text queries. Apache Lucene underlies Hibernate Search.

5.2.2. Integration with Hibernate Annotations

Hibernate Search integrates with Hibernate Annotations transparently provided that hibernate-search.jar is present in the classpath. If you do not wish to automatically register Hibernate Search event listeners, you can set hibernate.search.autoregister_listeners to false. Such a need is very uncommon and not recommended.
Check the Hibernate Search reference documentation for more information.

Revision History

Revision History
Revision 1.0-6.4002013-10-30Rüdiger Landmann
Rebuild with publican 4.0.0
Revision 1.0-62012-07-18Anthony Towns
Rebuild for Publican 3.0
Revision 1.0-0Thu Nov 19 2009Laura Bailey
Initial draft.