Revision as of 14:22, 21 June 2010

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:

• @OneToOne
• @OneToMany
• @ManyToOne
• @ManyToMany
• @BasicCollection
• @BasicMap

 
 @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.

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

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;
     }
     ...
 }

Common Relationship Configurations	Common Relationship Configurations	Collection Mappings
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