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Difference between revisions of "EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Relationship Mappings/Common Relationship Configurations/JoinFetch"
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Using the <tt>@JoinFetch</tt> annotation, you can enable the joining and reading of the related objects in the same query as the source object. | Using the <tt>@JoinFetch</tt> annotation, you can enable the joining and reading of the related objects in the same query as the source object. | ||
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| − | <span id="Example | + | The following example shows how to use the <tt>@JoinFetch</tt> annotation to specify <tt>Employee</tt> field <tt>managedEmployees</tt>. |
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@Entity | @Entity | ||
Revision as of 15:16, 29 March 2011
EclipseLink JPA
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Key API
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:
Using the @JoinFetch annotation, you can enable the joining and reading of the related objects in the same query as the source object.
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.
| 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:
For more information, see the following: |
JoinFetchType.INNER | No |
The following example shows how to use the @JoinFetch annotation to specify Employee field managedEmployees.
Example: @JoinFetch Annotation
@Entity public class Employee implements Serializable { ... @OneToMany(cascade=ALL, mappedBy="owner") @JoinFetch(value=OUTER) public Collection<Employee> getManagedEmployees() { return managedEmployees; } ... }
