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Red Hat Training
A Red Hat training course is available for JBoss Enterprise Application Platform Common Criteria Certification
Hibernate Annotations Reference Guide
JBoss Enterprise Application Platform Common Criteria Certification 5
for Use with JBoss Enterprise Application Platform 5 Common Criteria Certification
Edition 5.1.0
Red Hat Documentation Group
Copyright © 2011 Red Hat, Inc
Abstract
The Hibernate Annotations Reference Guide for JBoss Enterprise Application Platform 5.1.0.
Preface
Hibernate, like all other object/relational mapping tools, requires metadata that governs the transformation of data from one representation to the other. In Hibernate 2.x mapping metadata is most of the time declared in XML text files. Alternatively XDoclet can be used utilizing Javadoc source code annotations together with a compile time preprocessor.
The same kind of annotation support is now available in the standard JDK, although more powerful and with better tools support. IntelliJ IDEA and Eclipse for example, support auto-completion and syntax highlighting of JDK 5.0 annotations which are compiled into the bytecode and read at runtime using reflection. No external XML files are needed.
The EJB3 specification recognizes the interest and the success of the transparent object/relational mapping paradigm. It 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 and together with Hibernate Annotations offers 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. At all times you cann fall back to Hibernate native APIs, or if required, even to native JDBC and SQL.
Chapter 1. Setting up an annotations project
1.1. Requirements
- This release requires Hibernate Core 3.3 and above.
- This release is known to work on Hibernate Core 3.3.2.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.
1.2. 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
andlib/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.
1.3. Properties
Asides from the Hibernate core properties, Hibernate Annotations reacts to the following one
1.4. Logging
Hibernate Annotations utilizes Simple Logging Facade for Java (SLF4J) in order to log various system events. SLF4J can direct your logging output to several logging frameworks (NOP, Simple, log4j version 1.2, JDK 1.4 logging, JCL or logback) depending on your chosen binding. In order to setup logging properly you will need
slf4j-api.jar
in your classpath together with the jar file for your preferred binding - slf4j-log4j12.jar
in the case of Log4J. See the SLF4J documentation for more detail.
The logging categories interesting for Hibernate Annotations are:
Table 1.1. Hibernate Annotations Log Categories
Category | Function |
---|---|
org.hibernate.cfg | Log all configuration related events (not only annotations). |
For further category configuration refer to the Logging in the Hibernate Core documentation.
Chapter 2. Entity Beans
2.1. Intro
This section covers EJB 3.0 (aka Java Persistence) entity annotations and Hibernate-specific extensions.
2.2. 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 inspiration source.
2.2.1. 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, i.e. 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
.
2.2.1.1. 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 a 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.
2.2.1.2. 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 support 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 Entity Manager's reference documentation
LockMode.WRITE
2.2.2. Mapping simple properties
2.2.2.1. 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 support property mapping of all basic types supported by Hibernate (all basic Java types , their respective wrappers and serializable classes). Hibernate Annotations support 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 overriden 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.
2.2.2.2. 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

name (optional): the column name (default to the property name)
| |
unique (optional): set a unique constraint on this column or not (default false)
| |
nullable (optional): set the column as nullable (default true).
| |
insertable (optional): whether or not the column will be part of the insert statement (default true)
| |
updatable (optional): whether or not the column will be part of the update statement (default true)
| |
columnDefinition (optional): override the sql DDL fragment for this particular column (non portable)
| |
table (optional): define the targeted table (default primary table)
| |
(optional): column length (default 255)
| |
(optional): column decimal precision (default 0)
| |
(optional): column decimal scale if useful (default 0)
|
2.2.2.3. 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 inherit the access type of its owning entity (note that you can override that using the Hibernate specific
@AccessType
annotations (see Section 2.4, “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 informations).
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.
2.2.2.4. 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
2.2.3. 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 - either 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 2.4, “Hibernate Annotation Extensions” for more informations.
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 3, 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 thegenerators, 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 2.4.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; }
2.2.4. 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.
2.2.4.1. 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 work 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 support 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
.
2.2.4.2. 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.
2.2.4.3. 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
.
2.2.4.4. 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.
2.2.5. Mapping entity bean associations/relationships
2.2.5.1. 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 keys 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 a 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 don't have to (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.
2.2.5.2. 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;
}
...
}
2.2.5.3. Collections
2.2.5.3.1. 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 (ie 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 (eg 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 2.4, “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 represent 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 2.4, “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 informations.
Hibernate has several notions of collections.
Table 2.1. 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 2.4, “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 Street
s that are ordered by streetName
(of Street
) when the collection is loaded. Software
has a map of Version
s which key is the Version
codeName
.
Unless the collection is a generic, you will have to define
targetEntity
. This is a annotation attribute that take the target entity class as a value.
2.2.5.3.2. One-to-many
One-to-many associations are declared at the property level with the annotation
@OneToMany
. One to many associations may be bidirectional.
2.2.5.3.2.1. 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 don't have to (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() { ... }
2.2.5.3.2.2. 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
.
2.2.5.3.2.3. 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
).
2.2.5.3.2.4. 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).
2.2.5.3.3. Many-to-many
2.2.5.3.3.1. 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.
2.2.5.3.3.2. 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.
2.2.5.4. 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 2.4.7, “Cascade” for more information
Please refer to the chapter 6.3 of the EJB3 specification for more information on cascading and create/merge semantics.
2.2.5.5. 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 2.4.5.1, “Lazy options and fetching modes”.
The recommanded approach is to use
LAZY
onn 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.
2.2.6. 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 2.2.3, “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
inherit 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
.
2.2.7. 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.
2.3. Mapping Queries
2.3.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 availabe Hibernate hints are
Table 2.2. 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 |
2.3.2. Mapping native queries
You can also map a native query (ie 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 mappings 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 involve 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 Hibernate supports the dotted notation for embedded objects (you can even have nested embedded objects). EJB3 implementations do not have to support this feature, we do :-)
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 that common though).
@SqlResultSetMapping(name="scalar", columns=@ColumnResult(name="dimension")) @NamedNativeQuery(name="scalar", query="select length*width as dimension from SpaceShip", resultSetMapping="scalar")
An other 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.
2.4. 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.
2.4.1. 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 statetement.
@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, not a replacement to @javax.persistence.Table
. Especially, 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 or collection as immutable. An immutable entity may not be updated by the application. This allows Hibernate to make some minor performance optimizations. Updates to an immutable entity will be ignored, but no exception is thrown. @Immutable
must be used on root entities only. @Immutable
placed on a collection makes the collection immutable, meaning additions and deletions to and from the collection are not allowed. A HibernateException
is thrown in this case.
@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 { ... }
2.4.Identifier. Identifier
Hibernate Annotations goes beyond the Java Persistence specification when defining identifiers.
2.4.Identifier.1. Generators
@org.hibernate.annotations.GenericGenerator
and @org.hibernate.annotations.GenericGenerators
allows you to define an 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 an 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
2.4.Identifier.2. @NaturalId
While not used as identifier property, some (group of) properties represent 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).
2.4.3. Property
2.4.3.1. 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 overriden for the annotated element, if overriden 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 russian 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;
}
}
2.4.3.2. 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.
2.4.3.3. 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 informations on the Hibernate types.
@org.hibernate.annotations.TypeDef
and @org.hibernate.annotations.TypeDefs
allows you to declare type definitions. These annotations can be placed at the class or package level. Note that these definitions are be global for the session factory (even when defined at the class level). Type definitions have to be defined before any usage. If the type is used on a single entity, you can plance the definition on the entity itself. Otherwise, it is recommended to place the definition a the package level since the entity processing order is not guaranteed.
Note
Package level annotations are placed in a file named
package-info.java
in the appropriate package. Place your annotations before the package declaration.
//in org/hibernate/test/annotations/entity/package-info.java @TypeDefs( { @TypeDef( name="caster", typeClass = CasterStringType.class, parameters = { @Parameter(name="cast", value="lower") } ) } ) package org.hibernate.test.annotations.entity; //in org/hibernate/test/annotations/entity/Forest.java 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; ... }
2.4.3.4. 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; }
2.4.3.5. @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
2.4.3.6. 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
.
2.4.3.7. @Target
Sometimes, the type guessed by reflection is not the one you want Hibernate to use. This is especially true on 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;
}
2.4.3.8. 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, specifies that updates to this property do not require acquisition of the optimistic lock.
2.4.4. 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
.
2.4.5. 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, while generated by Hibernate, have a fairly unreadable name. You can override the constraint name by use
@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
2.4.5.1. Lazy options and fetching modes
EJB3 comes with the
fetch
option to define lazy loading and fetching modes, however Hibernate has a much more 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 bePROXY
(ie use a proxy based lazy loading),NO_PROXY
(use a bytecode enhancement based lazy loading - note that build time bytecode processing is necessary) andFALSE
(association not lazy)@LazyCollection
: defines the lazyness option on@ManyTo
Many and@OneToMany
associations. LazyCollectionOption can beTRUE
(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 beSELECT
(a select is triggered when the association needs to be loaded),SUBSELECT
(only available for collections, use a subselect strategy - please refers to the Hibernate Reference Documentation for more information) orJOIN
(use a SQL JOIN to load the association while loading the owner entity).JOIN
overrides any lazy attribute (an association loaded through aJOIN
strategy cannot be lazy).
The Hibernate annotations overrides the EJB3 fetching options.
Table 2.3. 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) |
2.4.5.2. @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; }
2.4.6. Collection related annotations
2.4.6.1. 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 implementorg.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 informations.
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
2.4.6.2. Extra collection types
2.4.6.2.1. 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
.
2.4.6.2.2. 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 override 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
allows 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>();
2.4.6.2.3. Bidirectional association with indexed collections
A bidirectional association where one end is an indexed collection (ie. 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.
2.4.6.2.4. Bag with primary key
Another interesting feature is the ability to define a surrogate primary key to a bag collection. This remove 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 a 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();
...
}
2.4.6.2.5. 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
2.4.6.2.6. @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() {
2.4.7. 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.
2.4.8. 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";
)
usage: the given cache concurrency strategy (NONE, READ_ONLY, NONSTRICT_READ_WRITE, READ_WRITE, TRANSACTIONAL)
| |
region (optional): the cache region (default to the fqcn of the class or the fq role name of the collection)
| |
include (optional): all to include all properties, non-lazy to only include non lazy properties (default all).
|
2.4.9. 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 use 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 >= requiredLevel") public Set<Forest> getForests() { ... }
2.4.10. 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 some attributes to the standard version and can be used as a replacement:
- flushMode: define 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.
2.4.11. 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 parameters order is important and is defined by the order Hibernate handle 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 to not 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 (promary or secondary): This comment will be used for DDL generation.
2.4.12. 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 correpsonding 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 3. 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 describes in hbm files.
The unit test suite shows some additional XML file samples.
3.1. 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 ot more XML files describing your metadata, these files will be merged by the overriding engine.
3.1.1. 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 (ie 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.
3.1.2. Entity level metadata
You can either define or override metadata informations on a given entity.
<?xml version="1.0" encoding="UTF-8"?> <entity-mappingsxmlns="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>
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.
| |
package (optional): default package used for all non qualified class names in the given deployment descriptor file.
| |
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 medatada complete element, if access is not defined, the @Id position will lead position, if access is defined, the value is used.
| |
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
| |
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.
| |
id-class : defines the id class in a similar way @IdClass does
| |
inheritance : defines the inheritance strategy (JOINED , TABLE_PER_CLASS , SINGLE_TABLE ), Available only at the root entity level
| |
sequence-generator : defines a sequence generator
| |
table-generator : defines a table generator
| |
: 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>
discriminator-value / discriminator-column : defines the discriminator value and the column holding it when the SINGLE_TABLE inheritance strategy is chosen
| |
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.
| |
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.
| |
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
| |
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>
.
3.1.3. 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 subelements accordingly: lob
, temporal
, enumerated
, column
.
3.1.4. 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 subelements accordingly: join-table
(which can have join-column
s and inverse-join-column
s), join-column
s
, 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 informations in the chapter describing annotations.
Chapter 4. Additional modules
Hibernate Annotations mainly focus on persistence metadata. The project also have a nice integration with two Hibernate modules.
4.1. Hibernate Validator
4.1.1. 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 metamodel 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 metamodel, 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
.
4.1.2. Integration with Hibernate Annotations
If Hibernate Validator (
hibernate-validator.jar
) is available in the classpath, Hibernate Annotations will integrate 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.
4.2. Hibernate Search
4.2.1. Description
Full text search engines like Apache Lucene are a very powerful technology to bring free text/efficient queries to applications. If 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. Hibernate Search is using Apache Lucene under the cover.
4.2.2. 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.
Appendix A. Revision History
Revision History | ||||
---|---|---|---|---|
Revision 5.1.0-110.33.400 | 2013-10-31 | Rüdiger Landmann | ||
| ||||
Revision 5.1.0-110.33 | July 24 2012 | Ruediger Landmann | ||
| ||||
Revision 5.1-0 | Wed Sep 15 2010 | Laura Bailey | ||
|
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