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Difference between revisions of "EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Relationship Mappings/Common Relationship Configurations/JoinFetch"

m (Fetch Type)
m (Fetch Type)
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You are not required to provide value for this attribute.
 
You are not required to provide value for this attribute.
  
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==What You May Need to Know About EclipseLink JPA Lazy Loading==
  
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JPA specifies that lazy loading is a hint to the persistence provider that data should be fetched lazily when it is first accessed, if possible.
 +
 +
If you are developing your application in a Java EE environment, you only have to set fetch to <tt>javax.persistence.FetchType.LAZY</tt>, and EclipseLink persistence provider will supply all the necessary functionality.
 +
 +
When using a [[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@OneToOne|one-to-one]] or [[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@ManyToOne|many-to-one]] mapping in a Java SE environment, to configure EclipseLink JPA to perform lazy loading when the <tt>fetch</tt> attribute is set to <tt>FetchType.LAZY</tt>, configure either dynamic or static weaving.
 +
 +
When using a [[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@OneToOne|one-to-one]] or [[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@ManyToOne|many-to-one]] mapping in a Java SE environment that does not permit the use of <tt>-javaagent</tt> on the JVM command line, to configure EclipseLink JPA to perform lazy loading when annotation attribute <tt>fetch</tt> is set to <tt>javax.persistence.FetchType.LAZY</tt>, you can use static weaving.
 +
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The [[#Table 19-33|EclipseLink JPA Support for Lazy Loading by Mapping Type]] table lists EclipseLink JPA support for lazy loading by mapping type.
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For more information, see the following:
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* [[#How to Configure Dynamic Weaving for JPA Entities Using the EclipseLink Agent|How to Configure Dynamic Weaving for JPA Entities Using the EclipseLink Agent]]
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* [[#How to Configure Static Weaving for JPA Entities|How to Configure Static Weaving for JPA Entities]]
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* [[#How to Disable Weaving Using EclipseLink Persistence Unit Properties|How to Disable Weaving Using EclipseLink Persistence Unit Properties]]
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* [[#What You May Need to Know About Weaving JPA Entities|What You May Need to Know About Weaving JPA Entities]]
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* [[Configuring%20a%20Mapping%20(ELUG)#Configuring Indirection (Lazy Loading)|Configuring Indirection (Lazy Loading)]]
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 +
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<span id="Table 19-33"></span>
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''''' EclipseLink JPA Support for Lazy Loading by Mapping Type'''''
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{| class="RuleFormalWideMax" dir="ltr" title="EclipseLink JPA Support for Lazy Loading by Mapping Type" summary="This table lists EclipseLink JPA mapping support for lazy loading by mapping type for Java EE (in container) and Java SE (outside of container) applications." width="100%" border="1" frame="border" rules="all" cellpadding="3" frame="border" rules="all"
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|- align="left" valign="top"
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! id="r1c1-t52" align="left" valign="bottom" | '''Mapping'''
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! id="r1c2-t52" align="left" valign="bottom" | '''Java EE''' <sup> 1 </sup>
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! id="r1c3-t52" align="left" valign="bottom" | '''Java SE'''
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|- align="left" valign="top"
 +
| id="r2c1-t52" headers="r1c1-t52" align="left" |
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[[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@ManyToMany|many-to-many]]
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| headers="r2c1-t52 r1c2-t52" align="left" |
 +
EclipseLink JPA performs lazy loading when the <tt>fetch</tt> attribute is set to <tt>javax.persistence.FetchType.LAZY</tt> (default).
 +
| headers="r2c1-t52 r1c3-t52" align="left" |
 +
EclipseLink JPA performs lazy loading when the <tt>fetch</tt> attribute is set to <tt>javax.persistence.FetchType.LAZY</tt> (default).
 +
|- align="left" valign="top"
 +
| id="r3c1-t52" headers="r1c1-t52" align="left" |
 +
[[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@OneToMany|one-to-many]]
 +
| headers="r3c1-t52 r1c2-t52" align="left" |
 +
EclipseLink JPA performs lazy loading when the <tt>fetch</tt> attribute is set to <tt>javax.persistence.FetchType.LAZY</tt> (default).
 +
| headers="r3c1-t52 r1c3-t52" align="left" |
 +
EclipseLink JPA performs lazy loading when the <tt>fetch</tt> attribute is set to <tt>javax.persistence.FetchType.LAZY</tt> (default).
 +
|- align="left" valign="top"
 +
| id="r4c1-t52" headers="r1c1-t52" align="left" |
 +
[[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@OneToOne|one-to-one]]
 +
| headers="r4c1-t52 r1c2-t52" align="left" |
 +
EclipseLink JPA performs lazy loading when the <tt>fetch</tt> attribute is set to <tt>javax.persistence.FetchType.LAZY</tt>.
 +
| headers="r4c1-t52 r1c3-t52" align="left" |
 +
By default, EclipseLink JPA ignores the <tt>fetch</tt> attribute and default javax.persistence.<tt>FetchType.EAGER</tt> applies.
 +
 +
To configure EclipseLink JPA to perform lazy loading when the <tt>fetch</tt> attribute set to <tt>FetchType.LAZY</tt>, consider one of the following:
 +
* [[#How to Configure Dynamic Weaving for JPA Entities Using the EclipseLink Agent|How to Configure Dynamic Weaving for JPA Entities Using the EclipseLink Agent]]
 +
* [[#How to Configure Static Weaving for JPA Entities|How to Configure Static Weaving for JPA Entities]]
 +
|- align="left" valign="top"
 +
| id="r5c1-t52" headers="r1c1-t52" align="left" |
 +
[[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@ManyToOne|many-to-one]]
 +
| headers="r5c1-t52 r1c2-t52" align="left" |
 +
EclipseLink JPA performs lazy loading when the <tt>fetch</tt> attribute is set to <tt>javax.persistence.FetchType.LAZY</tt>.
 +
| headers="r5c1-t52 r1c3-t52" align="left" |
 +
By default, EclipseLink JPA ignores the <tt>fetch</tt> attribute and default <tt>javax.persistence.FetchType.EAGER</tt> applies.
 +
 +
To configure EclipseLink JPA to perform lazy loading when the <tt>fetch</tt> attribute set to <tt>FetchType.LAZY</tt>, configure one of the following:
 +
* [[#How to Configure Dynamic Weaving for JPA Entities Using the EclipseLink Agent|How to Configure Dynamic Weaving for JPA Entities Using the EclipseLink Agent]]
 +
* [[#How to Configure Static Weaving for JPA Entities|How to Configure Static Weaving for JPA Entities]]
 +
|- align="left" valign="top"
 +
| id="r6c1-t52" headers="r1c1-t52" align="left" |
 +
[[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@Basic|basic]]
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| headers="r6c1-t52 r1c2-t52" align="left" |
 +
EclipseLink JPA performs lazy loading when the <tt>fetch</tt> attribute is set to <tt>javax.persistence.FetchType.LAZY</tt>.
 +
| headers="r6c1-t52 r1c3-t52" align="left" |
 +
By default, EclipseLink JPA ignores the <tt>fetch</tt> attribute and default javax.persistence.<tt>FetchType.EAGER</tt> applies.
 +
 +
To configure EclipseLink JPA to perform lazy loading when the <tt>fetch</tt> attribute set to <tt>FetchType.LAZY</tt>, consider one of the following:
 +
* [[#How to Configure Dynamic Weaving for JPA Entities Using the EclipseLink Agent|How to Configure Dynamic Weaving for JPA Entities Using the EclipseLink Agent]]
 +
* [[#How to Configure Static Weaving for JPA Entities|How to Configure Static Weaving for JPA Entities]]
 +
|}
 +
<br><sup> 1 </sup>Fully supported in any container that implements the appropriate container contracts in the EJB 3.0 specification.<br>
  
 
{{EclipseLink_JPA
 
{{EclipseLink_JPA

Revision as of 14:28, 15 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.

What You May Need to Know About EclipseLink JPA Lazy Loading

JPA specifies that lazy loading is a hint to the persistence provider that data should be fetched lazily when it is first accessed, if possible.

If you are developing your application in a Java EE environment, you only have to set fetch to javax.persistence.FetchType.LAZY, and EclipseLink persistence provider will supply all the necessary functionality.

When using a one-to-one or many-to-one mapping in a Java SE environment, to configure EclipseLink JPA to perform lazy loading when the fetch attribute is set to FetchType.LAZY, configure either dynamic or static weaving.

When using a one-to-one or many-to-one mapping in a Java SE environment that does not permit the use of -javaagent on the JVM command line, to configure EclipseLink JPA to perform lazy loading when annotation attribute fetch is set to javax.persistence.FetchType.LAZY, you can use static weaving.

The EclipseLink JPA Support for Lazy Loading by Mapping Type table lists EclipseLink JPA support for lazy loading by mapping type.

For more information, see the following:


EclipseLink JPA Support for Lazy Loading by Mapping Type

Mapping Java EE 1 Java SE

many-to-many

EclipseLink JPA performs lazy loading when the fetch attribute is set to javax.persistence.FetchType.LAZY (default).

EclipseLink JPA performs lazy loading when the fetch attribute is set to javax.persistence.FetchType.LAZY (default).

one-to-many

EclipseLink JPA performs lazy loading when the fetch attribute is set to javax.persistence.FetchType.LAZY (default).

EclipseLink JPA performs lazy loading when the fetch attribute is set to javax.persistence.FetchType.LAZY (default).

one-to-one

EclipseLink JPA performs lazy loading when the fetch attribute is set to javax.persistence.FetchType.LAZY.

By default, EclipseLink JPA ignores the fetch attribute and default javax.persistence.FetchType.EAGER applies.

To configure EclipseLink JPA to perform lazy loading when the fetch attribute set to FetchType.LAZY, consider one of the following:

many-to-one

EclipseLink JPA performs lazy loading when the fetch attribute is set to javax.persistence.FetchType.LAZY.

By default, EclipseLink JPA ignores the fetch attribute and default javax.persistence.FetchType.EAGER applies.

To configure EclipseLink JPA to perform lazy loading when the fetch attribute set to FetchType.LAZY, configure one of the following:

basic

EclipseLink JPA performs lazy loading when the fetch attribute is set to javax.persistence.FetchType.LAZY.

By default, EclipseLink JPA ignores the fetch attribute and default javax.persistence.FetchType.EAGER applies.

To configure EclipseLink JPA to perform lazy loading when the fetch attribute set to FetchType.LAZY, consider one of the following:


1 Fully supported in any container that implements the appropriate container contracts in the EJB 3.0 specification.

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