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| <title>Many-to-one mapping</title> |
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| <meta name="doctitle" content="Many-to-one mapping" /> |
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| <div class="sect2"><!-- infolevel="all" infotype="General" --> |
| <h1>Many-to-one mapping</h1> |
| <p><a id="sthref134" name="sthref134"></a><a id="sthref135" name="sthref135"></a><a id="sthref136" name="sthref136"></a><a id="sthref137" name="sthref137"></a>Use a <span class="bold">Many-to-One</span> mapping to defines a single-valued association to another entity class that has many-to-one multiplicity.</p> |
| <ol> |
| <li> |
| <p>In the <a href="ref_persistence_outline.htm#BABEGGFE">JPA Structure view</a>, select the field to map.</p> |
| </li> |
| <li> |
| <p>Right click the field and then select <span class="bold">Map As > Many-to-One</span>. The <a href="ref_persistence_map_view.htm#BABIFBAF">JPA Details view (for attributes)</a> displays the properties for the selected.</p> |
| </li> |
| <li> |
| <p>Use this table to complete the <a href="ref_mapping_general.htm#CACBHFIJ">General information</a> fields JPA Details view.</p> |
| <div class="inftblruleinformal"> |
| <table class="RuleInformal" title="This table lists the fields ion the General tab for this mapping." summary="This table lists the fields ion the General tab for this mapping." dir="ltr" border="1" width="100%" frame="border" rules="all" cellpadding="3" cellspacing="0"> |
| <col width="19%" /> |
| <col width="*" /> |
| <col width="41%" /> |
| <thead> |
| <tr align="left" valign="top"> |
| <th align="left" valign="bottom" id="r1c1-t21">Property</th> |
| <th align="left" valign="bottom" id="r1c2-t21">Description</th> |
| <th align="left" valign="bottom" id="r1c3-t21">Default</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr align="left" valign="top"> |
| <td align="left" id="r2c1-t21" headers="r1c1-t21">Mapping Entity Hyperlink</td> |
| <td align="left" headers="r2c1-t21 r1c2-t21">Defines mapping as <span class="bold">Many-to-One</span>. This corresponds to the <code>@ManyToOne</code> annotation.</td> |
| <td align="left" headers="r2c1-t21 r1c3-t21">Many-to-One</td> |
| </tr> |
| <tr align="left" valign="top"> |
| <td align="left" id="r3c1-t21" headers="r1c1-t21">Target Entity</td> |
| <td align="left" headers="r3c1-t21 r1c2-t21">The entity to which this attribute is mapped.</td> |
| <td align="left" headers="r3c1-t21 r1c3-t21">null |
| <p>You do not need to explicitly specify the target entity, since it can be inferred from the type of object being referenced.</p> |
| </td> |
| </tr> |
| <tr align="left" valign="top"> |
| <td align="left" id="r4c1-t21" headers="r1c1-t21">Fetch</td> |
| <td align="left" headers="r4c1-t21 r1c2-t21">Defines how data is loaded from the database. See <a href="ref_mapping_general.htm#CACGGGHB">"Fetch Type"</a> for details. |
| <ul> |
| <li> |
| <p>Eager</p> |
| </li> |
| <li> |
| <p>Lazy</p> |
| </li> |
| </ul> |
| </td> |
| <td align="left" headers="r4c1-t21 r1c3-t21">Eager</td> |
| </tr> |
| <tr align="left" valign="top"> |
| <td align="left" id="r5c1-t21" headers="r1c1-t21">Cascade</td> |
| <td align="left" headers="r5c1-t21 r1c2-t21">See <a href="ref_mapping_general.htm#CACJAIHB">"Cascade Type"</a> for details. |
| <ul> |
| <li> |
| <p>Default</p> |
| </li> |
| <li> |
| <p>All</p> |
| </li> |
| <li> |
| <p>Persist</p> |
| </li> |
| <li> |
| <p>Merge</p> |
| </li> |
| <li> |
| <p>Remove</p> |
| </li> |
| </ul> |
| </td> |
| <td align="left" headers="r5c1-t21 r1c3-t21">Default</td> |
| </tr> |
| <tr align="left" valign="top"> |
| <td align="left" id="r6c1-t21" headers="r1c1-t21">Optional</td> |
| <td align="left" headers="r6c1-t21 r1c2-t21">Specifies if this field is can be null.</td> |
| <td align="left" headers="r6c1-t21 r1c3-t21">Yes</td> |
| </tr> |
| </tbody> |
| </table> |
| <br /></div> |
| <!-- class="inftblruleinformal" --></li> |
| <li> |
| <p>Use this table to complete the fields on the <a href="reference012.htm#CACFCEJC">Join Columns Information</a> tab in the <span class="gui-object-title">JPA Details</span> view.</p> |
| <div class="inftblruleinformal"> |
| <table class="RuleInformal" title="This table lists the fields in the Persistence Properties view for this mapping." summary="This table lists the fields in the Persistence Properties view for this mapping." dir="ltr" border="1" width="100%" frame="border" rules="all" cellpadding="3" cellspacing="0"> |
| <col width="19%" /> |
| <col width="*" /> |
| <col width="41%" /> |
| <thead> |
| <tr align="left" valign="top"> |
| <th align="left" valign="bottom" id="r1c1-t22">Property</th> |
| <th align="left" valign="bottom" id="r1c2-t22">Description</th> |
| <th align="left" valign="bottom" id="r1c3-t22">Default</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr align="left" valign="top"> |
| <td align="left" id="r2c1-t22" headers="r1c1-t22">Join Column</td> |
| <td align="left" headers="r2c1-t22 r1c2-t22"><a id="sthref138" name="sthref138"></a><a id="sthref139" name="sthref139"></a>Specify a mapped column for joining an entity association. This field corresponds to the <code>@JoinColum</code> attribute. |
| <p>Select <span class="bold">Override Default</span>, then Add, Edit, or Remove the join columns.</p> |
| </td> |
| <td align="left" headers="r2c1-t22 r1c3-t22">By default, the mapping is assumed to have a single join.</td> |
| </tr> |
| </tbody> |
| </table> |
| <br /></div> |
| <!-- class="inftblruleinformal" --></li> |
| </ol> |
| <p>Eclipse adds the following annotations to the field:</p> |
| <pre xml:space="preserve" class="oac_no_warn"> |
| @JoinTable(joinColumns=@JoinColumn(name="<span class="italic"><JOIN_COLUMN></span>"), |
| name = "<span class="italic"><JOIN_TABLE_NAME></span>") |
| @ManyToOne(targetEntity=<span class="italic"><TARGET_ENTITY></span>, fetch=<span class="italic"><FETCH_TYPE></span>, |
| cascade=<span class="italic"><CASCADE_TYPE></span>) |
| </pre> |
| <p> </p> |
| <img src="img/ngrelt.png" alt="Related task" title="Related task" /><br /> |
| <br /> |
| <a href="task_mapping.htm#BABDGBIJ">Mapping an entity</a> |
| <p> </p> |
| <img src="img/ngrelr.png" alt="Related reference" title="Related reference" /><br /> |
| <br /> |
| <a href="ref_persistence_outline.htm#BABEGGFE">JPA Structure view</a><br /> |
| <a href="ref_persistence_map_view.htm#BABIFBAF">JPA Details view (for attributes)</a> |
| <p> </p> |
| <img src="img/ngrelc.png" alt="Related concept" title="Related concept" /><br /> |
| <br /> |
| <a href="concept_mapping.htm#BABBDJFI">Understanding OR mappings</a><br /> |
| <a href="concepts001.htm#BABBGFJG">Understanding EJB 3.0 Java Persistence API</a></div> |
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