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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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=Fetch Type=
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{{EclipseLink_UserGuide
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.
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|info=y
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|toc=n
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|eclipselink=y
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|eclipselinktype=JPA
  
You are not required to provide value for this attribute.
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|api=y
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|apis=
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* [http://www.eclipse.org/eclipselink/api/latest/org/eclipse/persistence/annotations/JoinFetch.html @JoinFetch]
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}}
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=@JoinFetch=
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Use the <tt>@JoinFetch</tt> annotation to enable the joining and reading of the related objects in the same query as the source object.
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{{EclipseLink_Note
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|note=We recommend setting join fetching at the query level, as not all queries require joining.
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}}
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You can specify the <tt>@JoinFetch</tt> annotation for the following mappings:
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* <tt>@OneToOne</tt>
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* <tt>[[EclipseLink/UserGuide/JPA/Basic_JPA_Development/Mapping/Relationship_Mappings/Collection_Mappings/OneToMany|@OneToMany]]</tt>
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* <tt>@ManyToOne</tt>
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* <tt>[[EclipseLink/UserGuide/JPA/Basic_JPA_Development/Mapping/Relationship_Mappings/Collection_Mappings/ManyToMany|@ManyToMany]]</tt>
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* <tt>@BasicCollection</tt> (deprecated)
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* <tt>@BasicMap</tt> (deprecated)
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Alternatively, you can use batch reading, especially for collection relationships.]].
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{{EclipseLink_AttributeTable
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|caption=@JoinFetch Annotation Attributes
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|content=<tr>
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<td>'''<tt>value</tt>'''</td>
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<td>Set this attribute to the <tt>org.eclipse.persistence.annotations.JoinFetchType</tt> enumerated type of the fetch that you will be using.
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The following are the valid values for the <tt>JoinFetchType</tt><nowiki>:</nowiki>
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* <tt>INNER</tt> – This option provides the inner join fetching of the related object.<br>Note: Inner joining does not allow for null or empty values.
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* <tt>OUTER</tt> – This option provides the outer join fetching of the related object.<br>Note: Outer joining allows for null or empty values.<br>
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</td>
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<td><tt>JoinFetchType.INNER</tt></td>
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<td>No</td>
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</tr>
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}}
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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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<span id="Example: @JoinFetch Annotation"></span>
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======''Example: @JoinFetch Annotation''======
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<source lang="java">
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@Entity
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public class Employee implements Serializable {
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    ...
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    @OneToMany(cascade=ALL, mappedBy="owner")
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    @JoinFetch(value=OUTER)
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    public Collection<Employee> getManagedEmployees() {
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        return managedEmployees;
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    }
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    ...
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}
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</source>
  
  
  
 
{{EclipseLink_JPA
 
{{EclipseLink_JPA
|previous= [[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Relationship_Mappings/Common_Relationship_Configuration|Common Relationship Configuration]]
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|previous= [[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Relationship_Mappings/Common_Relationship_Configurations|Common Relationship Configurations]]
 
|next=[[EclipseLink/UserGuide/JPA/Basic_JPA_Development/Mapping/Relationship_Mappings/Collection_Mappings|Collection Mappings]]
 
|next=[[EclipseLink/UserGuide/JPA/Basic_JPA_Development/Mapping/Relationship_Mappings/Collection_Mappings|Collection Mappings]]
|up=[[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Relationship_Mappings/Common_Relationship_Configuration|Common Relationship Configuration]]}}
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|up=[[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Relationship_Mappings/Common_Relationship_Configurations|Common Relationship Configurations]]
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|version=2.2.0 DRAFT}}

Latest revision as of 12:07, 17 May 2011

EclipseLink JPA

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Elug api package icon.png Key API

@JoinFetch

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

Elug note icon.png

Note: We recommend setting join fetching at the query level, as not all queries require joining.

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


Alternatively, you can use batch reading, especially for collection relationships.]].

@JoinFetch Annotation Attributes
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.


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;
     }
     ...
 }


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Version: 2.2.0 DRAFT
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