@JoinFetch

Use the @JoinFetch annotation to enable the joining and reading of the related objects in the same query as the source object.

Note:

You should set join fetching at the query level, as not all queries require joining.

Annotation Elements

Table 2-28 describes this annotation's elements.

Table 2-28 @JoinFetch Annotation Elements

Annotation Element Description Default

Annotation Element	Description	Default
`value`	(Optional) 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.	`JoinFetchType.INNER`

value

(Optional) 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.

JoinFetchType.INNER

Usage

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

@OneToOne
@OneToMany
@ManyToOne
@ManyToMany
@ElementCollection

Alternatively, you can use batch fetching which is more efficient, especially for collection relationships.

Examples

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

Example 2-52 Using @JoinFetch Annotation

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

Example 2-53 shows how to use this extension in the eclipselink-orm.xml file.

Example 2-53 Using <join-fetch> in XML

<one-to-many name="managedEmployees">
    <join-fetch>OUTER</join-fetch>
</one-to-many>

See Also

For more information, see:

Understanding EclipseLink
"Enhancing Performance" in Solutions Guide for EclispeLink
"@BatchFetch"