Notice: This Wiki is now read only and edits are no longer possible. Please see: https://gitlab.eclipse.org/eclipsefdn/helpdesk/-/wikis/Wiki-shutdown-plan for the plan.
Difference between revisions of "EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Relationship Mappings/Common Relationship Configurations/JoinFetch"
m |
m |
||
Line 1: | Line 1: | ||
− | {{EclipseLink_UserGuide|toc=y|api= | + | {{EclipseLink_UserGuide|toc=y|api=n |
|1=javax.persitence.FetchType | |1=javax.persitence.FetchType | ||
}} | }} | ||
Line 7: | Line 7: | ||
You are not required to provide value for this attribute. | You are not required to provide value for this attribute. | ||
− | ==How to | + | ==How to Use the @JoinFetch Annotation== |
− | + | ||
− | + | You can specify the <tt>@JoinFetch</tt> annotation for the following mappings: | |
− | + | * <tt>[[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@OneToOne|@OneToOne]]</tt> | |
− | < | + | * <tt>[[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@OneToMany|@OneToMany]]</tt> |
− | + | * <tt>[[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@ManyToOne|@ManyToOne]]</tt> | |
− | + | * <tt>[[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@ManyToMany|@ManyToMany]]</tt> | |
− | + | * <tt>[[#How to Use the @BasicCollection Annotation|@BasicCollection]]</tt> | |
− | + | * <tt>[[#How to Use the @BasicMap Annotation|@BasicMap]]</tt> | |
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
<source lang="java"> | <source lang="java"> | ||
− | + | @Target({METHOD, FIELD}) | |
− | + | @Retention(RUNTIME) | |
− | + | public @interface JoinFetch { | |
− | + | JoinFetchType value() default JoinFetchType.INNER; | |
− | + | } | |
− | + | ||
− | + | ||
− | + | ||
− | + | ||
</source> | </source> | ||
+ | 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. | ||
+ | {{EclipseLink_Note | ||
+ | |note=We recommend setting join fetching at the query level, as not all queries require joining. For more information, see [[Using%20Basic%20Query%20API%20(ELUG)#Using Join Reading with ObjectLevelReadQuery|Using Join Reading with ObjectLevelReadQuery]]. | ||
+ | }} | ||
− | + | Alternatively, you can use batch reading, especially for collection relationships. For more information, see [[Using%20Basic%20Query%20API%20(ELUG)#Using_Batch_Reading|Using Batch Reading]]. | |
− | + | {{EclipseLink_AttributeTable | |
+ | |caption=<span id="Table 19-4">This table lists attributes of the <tt>@JoinFetch</tt> annotation.</span> | ||
+ | |content=<tr> | ||
+ | <td>'''<tt>value</tt>'''</td> | ||
+ | <td>Set this attribute to the <tt>org.eclipse.persistence.annotations.JoinFetchType</tt> enumerated type of the fetch that you will be using. | ||
− | + | The following are the valid values for the <tt>JoinFetchType</tt><nowiki>:</nowiki> | |
+ | * <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. | ||
+ | * <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> | ||
+ | For more information, see the following: | ||
+ | * [[Introduction%20to%20EclipseLink%20Expressions%20(ELUG)#What You May Need to Know About Joins|What You May Need to Know About Joins]] | ||
+ | * [[Using%20Basic%20Query%20API%20(ELUG)#Using Join Reading with ObjectLevelReadQuery|Using Join Reading with ObjectLevelReadQuery]] | ||
+ | * [[Configuring%20a%20Relational%20Mapping%20(ELUG)#Configuring Joining at the Mapping Level|Configuring Joining at the Mapping Level]] | ||
+ | </td> | ||
+ | <td><tt>JoinFetchType.INNER</tt></td> | ||
+ | <td>No</td> | ||
+ | </tr> | ||
+ | }} | ||
− | < | + | This example shows how to use the <tt>@JoinFetch</tt> annotation to specify <tt>Employee</tt> field <tt>managedEmployees</tt>. |
− | + | ||
+ | <span id="Example 19-5"></span> | ||
+ | ''''' Usage of the @JoinFetch Annotation''''' | ||
<source lang="java"> | <source lang="java"> | ||
− | + | @Entity | |
− | + | public class Employee implements Serializable { | |
− | + | ... | |
− | + | @OneToMany(cascade=ALL, mappedBy="owner") | |
− | + | @JoinFetch(value=OUTER) | |
− | + | public Collection<Employee> getManagedEmployees() { | |
− | + | return managedEmployees; | |
+ | } | ||
+ | ... | ||
+ | } | ||
</source> | </source> | ||
+ | |||
Revision as of 10:04, 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:
@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.
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 |
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; } ... }