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| <title>Many-to-many mapping</title> |
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| <meta name="doctitle" content="Many-to-many mapping" /> |
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| <p><a id="BABEIEGD" name="BABEIEGD"></a></p> |
| <div class="sect2"><!-- infolevel="all" infotype="General" --> |
| <h1>Many-to-many mapping</h1> |
| <p><a id="sthref130" name="sthref130"></a><a id="sthref131" name="sthref131"></a><a id="sthref132" name="sthref132"></a><a id="sthref133" name="sthref133"></a>Use a <span class="bold">Many-to-Many Mapping</span> to define a many-valued association with many-to-many multiplicity. A many-to-many mapping has two sides: the <span class="italic">owning side</span> and <span class="italic">non-owning side</span>. You must specify the join table on the owning side. For bidirectional mappings, either side may be the owning side.</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-Many</span>. The <a href="ref_persistence_map_view.htm#BABIFBAF">JPA Details view (for attributes)</a> displays the properties for the selected field.</p> |
| </li> |
| <li> |
| <p>Use this table to complete the <a href="ref_mapping_general.htm#CACBHFIJ">General information</a> fields of 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-t19">Property</th> |
| <th align="left" valign="bottom" id="r1c2-t19">Description</th> |
| <th align="left" valign="bottom" id="r1c3-t19">Default</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr align="left" valign="top"> |
| <td align="left" id="r2c1-t19" headers="r1c1-t19">Mapping Entity Hyperlink</td> |
| <td align="left" headers="r2c1-t19 r1c2-t19">Defines this mapping as a <span class="bold">Many to Many Mapping</span>. |
| <p>This field corresponds to the <code>@ManyToMany</code> annotation.</p> |
| </td> |
| <td align="left" headers="r2c1-t19 r1c3-t19">Many to Many</td> |
| </tr> |
| <tr align="left" valign="top"> |
| <td align="left" id="r3c1-t19" headers="r1c1-t19">Target Entity</td> |
| <td align="left" headers="r3c1-t19 r1c2-t19">The entity to which this attribute is mapped.</td> |
| <td align="left" headers="r3c1-t19 r1c3-t19">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-t19" headers="r1c1-t19">Fetch</td> |
| <td align="left" headers="r4c1-t19 r1c2-t19">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-t19 r1c3-t19">Lazy</td> |
| </tr> |
| <tr align="left" valign="top"> |
| <td align="left" id="r5c1-t19" headers="r1c1-t19">Mapped By</td> |
| <td align="left" headers="r5c1-t19 r1c2-t19">The database field that owns the relationship.</td> |
| <td align="left" headers="r5c1-t19 r1c3-t19"><br /></td> |
| </tr> |
| <tr align="left" valign="top"> |
| <td align="left" id="r6c1-t19" headers="r1c1-t19">Order By</td> |
| <td align="left" headers="r6c1-t19 r1c2-t19">Specify the default order for objects returned from a query. See <a href="ref_mapping_general.htm#CACDADIH">"Order By"</a> for details. |
| <ul> |
| <li> |
| <p>No ordering</p> |
| </li> |
| <li> |
| <p>Primary key</p> |
| </li> |
| <li> |
| <p>Custom</p> |
| </li> |
| </ul> |
| </td> |
| <td align="left" headers="r6c1-t19 r1c3-t19">No ordering</td> |
| </tr> |
| </tbody> |
| </table> |
| <br /></div> |
| <!-- class="inftblruleinformal" --></li> |
| <li> |
| <p>Use this table to complete the fields in the <a href="reference011.htm#CACBAEBC">Join Table Information</a> area 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 Join Table tab of the Persistence Properties view for this mapping." summary="This table lists the fields in the Join Table tab of 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="38%" /> |
| <thead> |
| <tr align="left" valign="top"> |
| <th align="left" valign="bottom" id="r1c1-t20">Property</th> |
| <th align="left" valign="bottom" id="r1c2-t20">Description</th> |
| <th align="left" valign="bottom" id="r1c3-t20">Default</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr align="left" valign="top"> |
| <td align="left" id="r2c1-t20" headers="r1c1-t20">Name</td> |
| <td align="left" headers="r2c1-t20 r1c2-t20">Name of the join table that contains the foreign key column.</td> |
| <td align="left" headers="r2c1-t20 r1c3-t20">You must specify the join table on the owning side. |
| <p>By default, the name is assumed to be the primary tables associated with the entities concatenated with an underscore.</p> |
| </td> |
| </tr> |
| <tr align="left" valign="top"> |
| <td align="left" id="r3c1-t20" headers="r1c1-t20">Join Columns</td> |
| <td align="left" headers="r3c1-t20 r1c2-t20">Select <span class="bold">Override Default</span>, then Add, Edit, or Remove the join columns.</td> |
| <td align="left" headers="r3c1-t20 r1c3-t20">By default, the name is assumed to be the primary tables associated with the entities concatenated with an underscore.</td> |
| </tr> |
| <tr align="left" valign="top"> |
| <td align="left" id="r4c1-t20" headers="r1c1-t20">Inverse Join Columns</td> |
| <td align="left" headers="r4c1-t20 r1c2-t20">Select <span class="bold">Override Default</span>, then Add, Edit, or Remove the join columns.</td> |
| <td align="left" headers="r4c1-t20 r1c3-t20">By default, the mapping is assumed to have a single join.</td> |
| </tr> |
| </tbody> |
| </table> |
| <br /></div> |
| <!-- class="inftblruleinformal" --></li> |
| <li> |
| <p>To add a new Join or Inverse Join Column, click <span class="gui-object-action">Add</span>.</p> |
| <p>To edit an existing Join or Inverse Join Column, select the field to and click <span class="gui-object-action">Edit</span>.</p> |
| </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>") |
| @ManyToMany(cascade=CascadeType.<span class="italic"><CASCADE_TYPE></span>, fetch=FetchType.<span class="italic"><FETCH_TYPE></span>, |
| targetEntity=<span class="italic"><TARGET_ENTITY></span>, mappedBy = "<span class="italic"><MAPPED_BY></span>") |
| @OrderBy("<span class="italic"><ORDER_BY></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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