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<title>One-to-many mapping</title>
 
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<meta name="doctitle" content="One-to-many mapping" />
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<p><a id="BABHGEBD" name="BABHGEBD"></a></p>
<div class="sect2"><!-- infolevel="all" infotype="General" -->
<h1>One-to-many mapping</h1>
<p><a id="sthref123" name="sthref123"></a><a id="sthref124" name="sthref124"></a><a id="sthref125" name="sthref125"></a><a id="sthref126" name="sthref126"></a>Use a <span class="bold">One-to-Many Mapping</span> to define a relationship with one-to-many multiplicity.</p>
<ol start="1">
<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; One-to-many</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 in the General tab of the Persistence Properties view for this mapping." summary="This table lists the fields in the General tab of the Persistence Properties view for this mapping." dir="ltr" border="1" width="100%" frame="border" rules="all" cellpadding="3" cellspacing="0">
<thead>
<tr align="left" valign="top">
<th align="left" valign="bottom" id="r1c1-t24">Property</th>
<th align="left" valign="bottom" id="r1c2-t24">Description</th>
<th align="left" valign="bottom" id="r1c3-t24">Default</th>
</tr>
</thead>
<tbody>
<tr align="left" valign="top">
<td align="left" id="r2c1-t24" headers="r1c1-t24">Mapping Entity Type Hyperlink</td>
<td align="left" headers="r2c1-t24 r1c2-t24">Defines mapping as <span class="bold">One-to-Many</span>. This corresponds to the <code>@OneToMany</code> annotation.</td>
<td align="left" headers="r2c1-t24 r1c3-t24">One-to-Many</td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r3c1-t24" headers="r1c1-t24">Target Entity</td>
<td align="left" headers="r3c1-t24 r1c2-t24">The entity to which this attribute is mapped.</td>
<td align="left" headers="r3c1-t24 r1c3-t24"><br /></td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r4c1-t24" headers="r1c1-t24">Cascade</td>
<td align="left" headers="r4c1-t24 r1c2-t24">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="r4c1-t24 r1c3-t24"><br /></td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r5c1-t24" headers="r1c1-t24">Fetch</td>
<td align="left" headers="r5c1-t24 r1c2-t24">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="r5c1-t24 r1c3-t24">Eager</td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r6c1-t24" headers="r1c1-t24">Mapped By</td>
<td align="left" headers="r6c1-t24 r1c2-t24">The database field that owns the relationship.</td>
<td align="left" headers="r6c1-t24 r1c3-t24"><br /></td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r7c1-t24" headers="r1c1-t24">Order By</td>
<td align="left" headers="r7c1-t24 r1c2-t24">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="r7c1-t24 r1c3-t24">No ordering</td>
</tr>
</tbody>
</table>
<br /></div>
<!-- class="inftblruleinformal" --></li>
<li>
<p>Use this table to complete the <a href="reference014.htm#CACBAEBC">Join Table Information</a> fields in the JPA Details 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">
<thead>
<tr align="left" valign="top">
<th align="left" valign="bottom" id="r1c1-t25">Property</th>
<th align="left" valign="bottom" id="r1c2-t25">Description</th>
<th align="left" valign="bottom" id="r1c3-t25">Default</th>
</tr>
</thead>
<tbody>
<tr align="left" valign="top">
<td align="left" id="r2c1-t25" headers="r1c1-t25">Name</td>
<td align="left" headers="r2c1-t25 r1c2-t25">Name of the join table</td>
<td align="left" headers="r2c1-t25 r1c3-t25">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="r3c1-t25" headers="r1c1-t25">Join Columns</td>
<td align="left" headers="r3c1-t25 r1c2-t25">Specify two or more join columns (that is, a primary key).</td>
<td align="left" headers="r3c1-t25 r1c3-t25"><br /></td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r4c1-t25" headers="r1c1-t25">Inverse Join Columns</td>
<td align="left" headers="r4c1-t25 r1c2-t25">The join column on the owned (or inverse) side of the association: the owned entity's primary key column.</td>
<td align="left" headers="r4c1-t25 r1c3-t25"><br /></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">
@OneToMany(targetEntity=<span class="italic">&lt;TARGET_ENTITY&gt;</span>)
@Column(name="<span class="italic">&lt;COLUMN&gt;</span>")


@OneToMany(targetEntity=<span class="italic">&lt;TARGET_ENTITY&gt;</span>.class, cascade=CascadeType.<span class="italic">&lt;CASCADE_TYPE&gt;</span>, 
    fetch = FetchType.<span class="italic">&lt;FETCH_TYPE&gt;</span>, mappedBy = "<span class="italic">&lt;MAPPED_BY&gt;</span>")@OrderBy("<span class="italic">&lt;ORDER_BY&gt;</span>")
@JoinTable(name="<span class="italic">&lt;JOIN_TABLE_NAME&gt;</span>", joinColumns=@JoinColumn(name=
    "<span class="italic">&lt;JOIN_COLUMN_NAME&gt;</span>", referencedColumnName="<span class="italic">&lt;JOIN_COLUMN_REFERENCED_COLUMN&gt;</span>"), 
    inverseJoinColumns=@JoinColumn(name="<span class="italic">&lt;INVERSE_JOIN_COLUMN_NAME&gt;</span>", 
    referencedColumnName="<span class="italic">&lt;INVERSE_JOIN_COLUMN_REFERENCED_COLUMN&gt;</span>"))

</pre>
<p>&nbsp;</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>&nbsp;</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>&nbsp;</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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