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Difference between revisions of "EclipseLink/UserGuide/JPA/2.4/a batchfetch"
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Use <code>@BatchFetch</code> to read objects related to a relationship mapping (such as one-to-one, one-to-many, many-to-one, many-to-many, and element collection) to be read in a single query. | Use <code>@BatchFetch</code> to read objects related to a relationship mapping (such as one-to-one, one-to-many, many-to-one, many-to-many, and element collection) to be read in a single query. | ||
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''' ''' | ''' ''' | ||
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===Annotation Elements=== | ===Annotation Elements=== | ||
| − | [[#CHDJBJBC|Table 2- | + | [[#CHDJBJBC|Table 2-3]] describes this annotation's elements. |
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| − | '''''Table 2- | + | '''''Table 2-3 @BatchFetch Annotation Elements''''' |
{| class="HRuleFormalWide" dir="ltr" title="@BatchFetch Annotation Elements" summary="This table describes the list of attributes for this annotation." width="100%" border="1" frame="hsides" rules="rows" cellpadding="3" frame="hsides" rules="rows" | {| class="HRuleFormalWide" dir="ltr" title="@BatchFetch Annotation Elements" summary="This table describes the list of attributes for this annotation." width="100%" border="1" frame="hsides" rules="rows" cellpadding="3" frame="hsides" rules="rows" | ||
|- align="left" valign="top" | |- align="left" valign="top" | ||
| − | ! id="r1c1- | + | ! id="r1c1-t6" align="left" valign="bottom" | '''Annotation Element''' |
| − | ! id="r1c2- | + | ! id="r1c2-t6" align="left" valign="bottom" | '''Description''' |
| − | ! id="r1c3- | + | ! id="r1c3-t6" align="left" valign="bottom" | '''Default''' |
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size | size | ||
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Default size of the batch fetch, used only when <code>BatchFetchType</code>=<code>IN</code> to definite number of keys in each <code>IN</code> clause | Default size of the batch fetch, used only when <code>BatchFetchType</code>=<code>IN</code> to definite number of keys in each <code>IN</code> clause | ||
| − | | headers="r2c1- | + | | headers="r2c1-t6 r1c3-t6" align="left" | |
<code>256</code> or the query's <code>pageSize</code> (for cursor queries) | <code>256</code> or the query's <code>pageSize</code> (for cursor queries) | ||
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| − | | id="r3c1- | + | | id="r3c1-t6" headers="r1c1-t6" align="left" | |
BatchFetchType | BatchFetchType | ||
| − | | headers="r3c1- | + | | headers="r3c1-t6 r1c2-t6" align="left" | |
(optional) The type of batch fetch to use: | (optional) The type of batch fetch to use: | ||
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* EXISTS | * EXISTS | ||
* IN | * IN | ||
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JOIN | JOIN | ||
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''' ''' | ''' ''' | ||
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Batch fetching allows for the optimal loading of a tree. Setting the <code>@BatchFetch</code> annotation on a ''child'' relationship of a tree structure causes EclipseLink to use a ''single'' SQL statement for each level. | Batch fetching allows for the optimal loading of a tree. Setting the <code>@BatchFetch</code> annotation on a ''child'' relationship of a tree structure causes EclipseLink to use a ''single'' SQL statement for each level. | ||
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''' ''' | ''' ''' | ||
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===Examples=== | ===Examples=== | ||
| − | + | The following examples show how to use this annotation with different batch fetch types. | |
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| − | '''''Example 2- | + | '''''Example 2-7 Using JOIN BatchFetch Type''''' |
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| − | '''''Example 2- | + | '''''Example 2-8 Using EXISTS BatchFetch Type''''' |
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| − | '''''Example 2- | + | '''''Example 2-9 Using IN BatchFetch Type''''' |
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For more information, see: | For more information, see: | ||
| − | * [[EclipseLink/UserGuide/JPA/a_joinfetch|"@JoinFetch"]] | + | * [[EclipseLink/UserGuide/JPA/2.4/a_joinfetch|"@JoinFetch"]] |
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| − | [[EclipseLink/UserGuide/JPA/a_cache|Next | + | [[EclipseLink/UserGuide/JPA/2.4/a_cache| Next ]][[Image:Elug_next_icon.png|Next]] |
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| − | [[Image:Eclipselink-logo.gif|150px|EclispeLink]]<br />[http:// | + | [[Image:Eclipselink-logo.gif|150px|EclispeLink]]<br />[[Image:Elug_home_icon.png|EclipseLink logo]] [http://www.eclipse.org/eclipselink/ EclipseLink Home] • [[Image:Elug_pdf.png|PDF]] PDF (coming soon)<br /> |
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| − | [http://www.google.com/cse/home?cx=016171230611334810008:y5kxq4rqd8s&hl=en Search] | + | [[Image:Elug_Magnifier.png|Search]][http://www.google.com/cse/home?cx=016171230611334810008:y5kxq4rqd8s&hl=en Search] |
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| − | [[EclipseLink/UserGuide/JPA/toc| Contents]] | + | [[Image:Elug_guide_icon.png|Contents]][[EclipseLink/UserGuide/JPA/2.4/toc| Contents]] |
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Revision as of 14:18, 19 June 2012
Java Persistence API (JPA) Extensions Reference for EclipseLink, 2.4.x
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Beta Draft: 2012-06-18
@BatchFetch
Use @BatchFetch to read objects related to a relationship mapping (such as one-to-one, one-to-many, many-to-one, many-to-many, and element collection) to be read in a single query.
Annotation Elements
Table 2-3 describes this annotation's elements.
Table 2-3 @BatchFetch Annotation Elements
| Annotation Element | Description | Default |
|---|---|---|
|
size |
Default size of the batch fetch, used only when |
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BatchFetchType |
(optional) The type of batch fetch to use:
|
JOIN |
Usage
Batch fetching allows for the optimal loading of a tree. Setting the @BatchFetch annotation on a child relationship of a tree structure causes EclipseLink to use a single SQL statement for each level.
Examples
The following examples show how to use this annotation with different batch fetch types.
Example 2-7 Using JOIN BatchFetch Type
Example 2-8 Using EXISTS BatchFetch Type
Example 2-9 Using IN BatchFetch Type
See Also
For more information, see:
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