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     <h1>JPA Usage

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     </h1>
 </div>

 <p><a name="JPAUsage-Thingstowatchoutfor"></a></p>

 <h1>Things to watch out for</h1>

 <p><a name="JPAUsage-Critical:Alwayssetjta-data-sourceandnon-jta-data-source"></a></p>

 <h2>Critical: Always set jta-data-source and non-jta-data-source</h2>

 <p>Always set the value of jta-data-source and non-jta-data-source in your
 persistence.xml file.  Regardless if targeting your EntityManager usage for
 transaction-type="RESOURCE_LOCAL" or transaction-type="TRANSACTION", it's
 very difficult to guarantee one or the other will be the only one needed.
 Often times the JPA Provider itself will require both internally to do
 various optimizations or other special features.  </p>

 <ul>
 <li>The <em>jta-data-source</em> should always have it's OpenEJB-specific
 '<em>JtaManaged</em>' property set to '<em>true</em>'  (this is the default)</li>
 <li>The <em>non-jta-data-source</em> should always have it's OpenEJB-specific
 '<em>JtaManaged</em>' property set to '<em>false</em>'.</li>
 </ul>

 <p>See <a href="containers-and-resources.html">Containers and Resources</a>
  for how to configure 'JtaManaged' and a full list of <Resource> properties
 for DataSources.</p>

 <p><a name="JPAUsage-Bedetachaware"></a></p>

 <h2>Be detach aware</h2>

 <p>A warning for any new JPA user is by default all objects will detach at the
 end of a transaction.  People typically discover this when the go to remove
 or update an object they fetched previously and get an exception like "You
 cannot perform operation delete on detached object".</p>

 <p>All ejb methods start a transaction unless a) you <a href="transaction-annotations.html">configure them otherwise</a>
 , or b) the caller already has a transaction in progress when it calls the
 bean.  If you're in a test case or a servlet, it's most likely B that is
 biting you.  You're asking an ejb for some persistent objects, it uses the
 EntityManager in the scope of the transaction started around it's method
 and returns some persistent objects, by the time you get them the
 transaction has completed and now the objects are detached.</p>

 <p><a name="JPAUsage-Solutions"></a></p>

 <h3>Solutions</h3>

 <ol>
 <li>Call EntityManager.merge(..) inside the bean code to reattach your
 object.</li>
 <li>Use PersistenceContextType.EXTENDED as in '@PersistenceContext(unitName
 = "movie-unit", type = PersistenceContextType.EXTENDED)' for EntityManager
 refs instead of the default of PersistenceContextType.TRANSACTION.</li>
 <li>If testing, use a technique to execute transactions in your test code.
 That's described here in <a href="unit-testing-transactions.html">Unit testing transactions</a></li>
 </ol>


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	<small><a href="./index.html">Home</a></small><br>
	<h1>JPA Usage

	<div style="float: right; position: relative; bottom: -10px; ">
	<a onclick="javascript:gpshare()" class="gp-share sprite" title="Share on Google+">share [gp]</a>
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	<a data-toggle="modal" href="#edit" class="edit-page" title="Contribute to this Page">contribute</a>
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	</h1>
	</div>

	<p><a name="JPAUsage-Thingstowatchoutfor"></a></p>

	<h1>Things to watch out for</h1>

	<p><a name="JPAUsage-Critical:Alwayssetjta-data-sourceandnon-jta-data-source"></a></p>

	<h2>Critical: Always set jta-data-source and non-jta-data-source</h2>

	<p>Always set the value of jta-data-source and non-jta-data-source in your
	persistence.xml file. Regardless if targeting your EntityManager usage for
	transaction-type="RESOURCE_LOCAL" or transaction-type="TRANSACTION", it's
	very difficult to guarantee one or the other will be the only one needed.
	Often times the JPA Provider itself will require both internally to do
	various optimizations or other special features. </p>

	<ul>
	<li>The <em>jta-data-source</em> should always have it's OpenEJB-specific
	'<em>JtaManaged</em>' property set to '<em>true</em>' (this is the default)</li>
	<li>The <em>non-jta-data-source</em> should always have it's OpenEJB-specific
	'<em>JtaManaged</em>' property set to '<em>false</em>'.</li>
	</ul>

	<p>See <a href="containers-and-resources.html">Containers and Resources</a>
	for how to configure 'JtaManaged' and a full list of <Resource> properties
	for DataSources.</p>

	<p><a name="JPAUsage-Bedetachaware"></a></p>

	<h2>Be detach aware</h2>

	<p>A warning for any new JPA user is by default all objects will detach at the
	end of a transaction. People typically discover this when the go to remove
	or update an object they fetched previously and get an exception like "You
	cannot perform operation delete on detached object".</p>

	<p>All ejb methods start a transaction unless a) you <a href="transaction-annotations.html">configure them otherwise</a>
	, or b) the caller already has a transaction in progress when it calls the
	bean. If you're in a test case or a servlet, it's most likely B that is
	biting you. You're asking an ejb for some persistent objects, it uses the
	EntityManager in the scope of the transaction started around it's method
	and returns some persistent objects, by the time you get them the
	transaction has completed and now the objects are detached.</p>

	<p><a name="JPAUsage-Solutions"></a></p>

	<h3>Solutions</h3>

	<ol>
	<li>Call EntityManager.merge(..) inside the bean code to reattach your
	object.</li>
	<li>Use PersistenceContextType.EXTENDED as in '@PersistenceContext(unitName
	= "movie-unit", type = PersistenceContextType.EXTENDED)' for EntityManager
	refs instead of the default of PersistenceContextType.TRANSACTION.</li>
	<li>If testing, use a technique to execute transactions in your test code.
	That's described here in <a href="unit-testing-transactions.html">Unit testing transactions</a></li>
	</ol>




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	<small>NOTICE: unless indicated otherwise on the pages in question, all editable content available from apache.org is presumed to be licensed under the Apache License (AL) version 2.0 and hence all submissions to apache.org treated as formal Contributions under the license terms.</small>
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