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EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Relationship Mappings/Common Relationship Configurations/JoinFetch



Fetch Type

By default, EclipseLink persistence provider uses a fetch type of javax.persitence.FetchType.EAGER: this is a requirement on the persistence provider runtime that data must be eagerly fetched.If the default is inappropriate for your application or a particular persistent field, set fetch to FetchType.LAZY: this is a hint to the persistence provider that data should be fetched lazily when it is first accessed (if possible). We recommend using the FetchType.LAZY on all relationships.

You are not required to provide value for this attribute.

How to Use the @JoinFetch Annotation

You can specify the @JoinFetch annotation for the following mappings:

 
 @Target({METHOD, FIELD})
 @Retention(RUNTIME)
 public @interface JoinFetch {
    JoinFetchType value() default JoinFetchType.INNER;
 }

Using the @JoinFetch annotation, you can enable the joining and reading of the related objects in the same query as the source object.

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Note: We recommend setting join fetching at the query level, as not all queries require joining. For more information, see Using Join Reading with ObjectLevelReadQuery.

Alternatively, you can use batch reading, especially for collection relationships. For more information, see Using Batch Reading.

This table lists attributes of the @JoinFetch annotation.
Attribute Description Default Required?
value Set this attribute to the org.eclipse.persistence.annotations.JoinFetchType enumerated type of the fetch that you will be using.

The following are the valid values for the JoinFetchType:

  • INNER – This option provides the inner join fetching of the related object.
    Note: Inner joining does not allow for null or empty values.
  • OUTER – This option provides the outer join fetching of the related object.
    Note: Outer joining allows for null or empty values.

For more information, see the following:

JoinFetchType.INNER No

This example shows how to use the @JoinFetch annotation to specify Employee field managedEmployees.

Usage of the @JoinFetch Annotation

 @Entity
 public class Employee implements Serializable {
     ...
     @OneToMany(cascade=ALL, mappedBy="owner")
     @JoinFetch(value=OUTER)
     public Collection<Employee> getManagedEmployees() {
         return managedEmployees;
     }
     ...
 }


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Version: 2.1.0
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