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<title>One-to-one mapping</title>
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<p><a id="BABFHBCJ" name="BABFHBCJ"></a></p>
<div class="sect2"><!-- infolevel="all" infotype="General" -->
<h1>One-to-one mapping</h1>
<p><a id="sthref144" name="sthref144"></a><a id="sthref145" name="sthref145"></a><a id="sthref146" name="sthref146"></a><a id="sthref147" name="sthref147"></a>Use a <span class="bold">One-to-One Mapping</span> to define a relationship with one-to-many 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 > One-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 in the JPA Details 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-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">Mapped Entity Hyperlink</td>
<td align="left" headers="r2c1-t25 r1c2-t25">Defines mapping as <span class="bold">One-to-One</span>. This corresponds to the <code>@OneToOne</code> annotation.</td>
<td align="left" headers="r2c1-t25 r1c3-t25">One-to-One</td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r3c1-t25" headers="r1c1-t25">Target Entity</td>
<td align="left" headers="r3c1-t25 r1c2-t25">The entity to which this attribute is mapped.</td>
<td align="left" headers="r3c1-t25 r1c3-t25">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-t25" headers="r1c1-t25">Fetch Type</td>
<td align="left" headers="r4c1-t25 r1c2-t25">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-t25 r1c3-t25">Eager</td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r5c1-t25" headers="r1c1-t25">Mapped By</td>
<td align="left" headers="r5c1-t25 r1c2-t25">The database field that owns the relationship.</td>
<td align="left" headers="r5c1-t25 r1c3-t25"><br /></td>
</tr>
</tbody>
</table>
<br /></div>
<!-- class="inftblruleinformal" --></li>
<li>
<p>Use this table to complete the <a href="reference012.htm#CACFCEJC">Join Columns Information</a> fields 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-t26">Property</th>
<th align="left" valign="bottom" id="r1c2-t26">Description</th>
<th align="left" valign="bottom" id="r1c3-t26">Default</th>
</tr>
</thead>
<tbody>
<tr align="left" valign="top">
<td align="left" id="r2c1-t26" headers="r1c1-t26">Join Column</td>
<td align="left" headers="r2c1-t26 r1c2-t26"><a id="sthref148" name="sthref148"></a><a id="sthref149" name="sthref149"></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-t26 r1c3-t26">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">
@OneToOne(targetEntity=<span class="italic"><TARGET_ENTITY></span>, cascade=CascadeType.<span class="italic"><CASCADE_TYPE></span>,
fetch = FetchType.<span class="italic"><FETCH_TYPE></span>, mappedBy = "<span class="italic"><MAPPED_BY></span>")
@JoinColumn(name="<span class="italic"><JOIN_COLUMN_NAME></span>", referencedColumnName=
"<span class="italic"><JOIN_COLUMN_REFERENCED_COLUMN></span>", insertable = <span class="italic"><INSERTABLE></span>,
updatable = <span class="italic"><UPDATABLE></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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