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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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<div class="sect2"><!-- infolevel="all" infotype="General" -->
<h1>Many-to-many mapping</h1>
<p><a id="sthref241" name="sthref241"></a><a id="sthref242" name="sthref242"></a><a id="sthref243" name="sthref243"></a><a id="sthref244" name="sthref244"></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 &gt; 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>
<div class="figure"><a id="sthref245" name="sthref245"></a>
<p class="titleinfigure">JPA Details, Many to many mapping</p>
<img src="img/jpa_details.manytomany.png" alt="JPA Details, Primary key generation" title="JPA Details, Primary key generation" /><br /></div>
<!-- class="figure" --></li>
<li>
<p>Complete each field in the <a href="reference038.htm#CACIHGCE">Many-to-Many Mapping</a> area.</p>
</li>
<li>
<p>Use the Joining Strategy area to specify the join strategy (or table) for the mapping.</p>
<div class="figure"><a id="sthref246" name="sthref246"></a>
<p class="titleinfigure">JPA Details, Joining Strategy</p>
<img src="img/jpa_details_joiningstrategy.png" alt="JPA Details, Joining Strategy" title="JPA Details, Joining Strategy" /><br /></div>
<!-- class="figure" --></li>
<li>
<p>Complete each field in the <a href="reference047.htm#CACIJEGI">Joining Strategy</a> area.</p>
</li>
<li>
<p>Complete the remaining areas in the <a href="ref_persistence_map_view.htm#BABIFBAF">JPA Details view (for attributes)</a>.</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">&lt;JOIN_COLUMN&gt;</span>"), 
    name = "<span class="italic">&lt;JOIN_TABLE_NAME&gt;</span>"
)
@ManyToMany(=Type.<span class="italic">&lt;_TYPE&gt;</span>, fetch=FetchType.<span class="italic">&lt;FETCH_TYPE&gt;</span>,
    targetEntity=<span class="italic">&lt;TARGET_ENTITY&gt;</span>, mappedBy = "<span class="italic">&lt;MAPPED_BY&gt;</span>")
@OrderBy("<span class="italic">&lt;ORDER_BY&gt;</span>")

</pre>
<a id="sthref247" name="sthref247"></a>
<p class="subhead2">Related tasks</p>
<ul>
<li>
<p><a href="task_mapping.htm#BABDGBIJ">Mapping an entity</a></p>
</li>
</ul>
<a id="sthref248" name="sthref248"></a>
<p class="subhead2">Related references</p>
<ul>
<li>
<p><a href="ref_persistence_outline.htm#BABEGGFE">JPA Structure view</a></p>
</li>
<li>
<p><a href="ref_persistence_map_view.htm#BABIFBAF">JPA Details view (for attributes)</a></p>
</li>
<li>
<p><a href="reference047.htm#CACIJEGI">Joining Strategy</a></p>
</li>
<li>
<p><a href="reference046.htm#CACBIJFD">Ordering</a></p>
</li>
<li>
<p><a href="reference053.htm#CIADGCID">Converters</a></p>
</li>
</ul>
<a id="sthref249" name="sthref249"></a>
<p class="subhead2">Related concepts</p>
<ul>
<li>
<p><a href="concept_mapping.htm#BABBDJFI">Understanding OR mappings</a></p>
</li>
<li>
<p><a href="concepts001.htm#BABBGFJG">Understanding Java Persistence API</a></p>
</li>
</ul>
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