⁠6.2. Boosting

Lucene has the notion of boosting which allows you to give certain documents or fields more or less importance than others. Lucene differentiates between index and search time boosting. The following sections show you how you can achieve index time boosting using Hibernate Search.
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⁠6.2.1. Static Index Time Boosting

To define a static boost value for an indexed class or property you can use the @Boost annotation. You can use this annotation within @Field or specify it directly on method or class level.
⁠

Example 6.10. Different ways of using @Boost

@Entity
@Indexed
@Boost(1.7f)
public class Essay {
    ...

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

    @Field(name="Abstract", store=Store.YES, boost=@Boost(2f))
    @Boost(1.5f)
    public String getSummary() { return summary; }

    @Lob
    @Field(boost=@Boost(1.2f))
    public String getText() { return text; }

    @Field
    public String getISBN() { return isbn; }

}
In Example 6.10, “Different ways of using @Boost”, Essay's probability to reach the top of the search list will be multiplied by 1.7. The summary field will be 3.0 (2 * 1.5, because @Field.boost and @Boost on a property are cumulative) more important than the isbn field. The text field will be 1.2 times more important than the isbn field. Note that this explanation is wrong in strictest terms, but it is simple and close enough to reality for all practical purposes.
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⁠6.2.2. Dynamic Index Time Boosting

The @Boostannotation used in Section 6.2.1, “Static Index Time Boosting” defines a static boost factor which is independent of the state of the indexed entity at runtime. However, there are usecases in which the boost factor may depend on the actual state of the entity. In this case you can use the @DynamicBoostannotation together with an accompanying custom BoostStrategy.
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Example 6.11. Dynamic boost example

​public enum PersonType {
​    NORMAL,
​    VIP
​}
​
​@Entity
​@Indexed
​@DynamicBoost(impl = VIPBoostStrategy.class)
​public class Person {
​    private PersonType type;   
​    
​    // ....
​}
​
​public class VIPBoostStrategy implements BoostStrategy {
​    public float defineBoost(Object value) {
​        Person person = ( Person ) value;
​        if ( person.getType().equals( PersonType.VIP ) ) {
​            return 2.0f;
​        }
​        else {
​            return 1.0f;
​        }
​    }
​}
In Example 6.11, “Dynamic boost example” a dynamic boost is defined on class level specifying VIPBoostStrategy as implementation of the BoostStrategy interface to be used at indexing time. You can place the @DynamicBoost either at class or field level. Depending on the placement of the annotation either the whole entity is passed to the defineBoost method or just the annotated field/property value. It's up to you to cast the passed object to the correct type. In the example all indexed values of a VIP person would be double as important as the values of a normal person.

Note

The specified BoostStrategy implementation must define a public no-arg constructor.
Of course you can mix and match @Boost and @DynamicBoost annotations in your entity. All defined boost factors are cumulative.
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