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OPENJPA-1742: add documentation 

git-svn-id: https://svn.apache.org/repos/asf/openjpa/branches/2.0.x@966702 13f79535-47bb-0310-9956-ffa450edef68
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Michael Dick 2010-07-22 15:06:07 +00:00
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openjpa-project/src/doc/manual/ref_guide_dbsetup.xml
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@ -370,6 +370,111 @@ properties are outlined in <xref linkend="ref_guide_conf"/>.
</programlisting> </programlisting>
</example> </example>
</section> </section>
<section id="ref_guide_dbsetup_setDSatRuntime">
<title>Setting the DataSource at runtime</title>
<indexterm zone="ref_guide_dbsetup_setDSatRuntime">
<primary>connections</primary>
<secondary>override configuration</secondary>
</indexterm>
<para>
As mentioned above, the JTA and Non-JTA DataSources may be passed in as configuration properties
at EntityManagerFactory creation. Either the JPA standard properties (
<literal>javax.persistence.jtaDataSource</literal>, <literal>java.persistence.nonJtaDataSource</literal>)
or their OpenJPA specific equivalents (<literal>openjpa.ConnectionFactoryName</literal>,
<literal>openjpa.ConnectionFactory2Name</literal>) may be used. One usecase for this function is to
store production connection information in configuration files but override the value when testing.
</para>
<para>
<example>
<programlisting>Map&lt;Object,Object&gt; props = new HashMap&lt;Object,Object&gt;();
props.put("javax.persistence.jtaDataSource", "jdbc/myDataSource");
props.put("javax.persistence.nonJtaDataSource", "jdbc/myNonJTADataSource");
emf = Persistence.createEntityManagerFactory("example", props);</programlisting>
</example>
</para>
<section id="ref_guide_dbsetup_setDSPerEM">
<title>Using different datasources for each EntityManager</title>
<para>
The JPA specification allows the DataSource (ConnectionFactory) to be specified on the
EntityManagerFactory.OpenJPA extends this support and allows each EntityManager to override the
DataSource from the EntityManagerFactory. It's expected that the EntityManagerFactory will also be
configured with a valid jta / nonJta DataSource. The DataSource configured on the
EntityManagerFactory will be used to obtain a DBDictionary and (rarely) to gather some information
about the database in use (e.g. version, JDBC driver version).
</para>
<para>
If the EntityManagerFactory is not configured with a valid DataSource there are
a few additional caveats.
<itemizedlist>
<listitem><para>The <literal>openjpa.DBDictionary</literal> property must be
used to ensure the correct DBDictionary is used.</para></listitem>
<listitem><para>OpenJPA will always attempt to obtain a datasource from JNDI
based on the configuration for the EntityManagerFactory. When a JNDI name is
specified on the EntityManager this lookup happens slightly earlier than
normal. If the lookup fails the JNDI name provided at EntityManager creation
will be set into the EntityManagerFactory's configuration and used in
subsequent attempts. </para></listitem>
</itemizedlist>
</para>
<section id="ref_guide_dbsetup_setDSBenefits">
<title>Benefits</title>
<para>
In effect this option allows a single set of entity definitions to be shared
between multiple database instances or schemas within an instance. This can be
highly beneficial when there are a large number of entity definitions (e.g. >
200), or a large number of databases / schemas in use.
</para>
</section>
<section id="ref_guide_dbsetup_setDSLimitations">
<title>Limitations</title>
<para>
<itemizedlist>
<listitem>
<para>The same database type and version must be used by each
EntityManager. OpenJPA will use the same DBDictionary for each
EntityManager and will make no attempt to alter SQL syntax
between EntityManager instances.
</para>
</listitem>
<listitem><para>It is the application's responsibility to ensure
that the schema is identical on each database.</para></listitem>
<listitem><para>The application may not specify schema names for
individual entities.</para></listitem>
<listitem>
<para>The DataSource (ConnectionFactory) name may only be
specified when the EntityManager is created. The datasource
may not be switched while an EntityManager is in use.
</para>
</listitem>
<listitem><para>The L2 cache (DataCache) should not be used if
different DataSources are specified for each EntityManager</para>
</listitem>
<listitem><para>SynchronizeMappings should not be used with this
feature.</para></listitem>
<listitem><para>Table and Sequence generators should not be used
with this feature.</para></listitem>
<listitem><para>It is not required, but is recommended that the
<literal>openjpa.DBDictionary</literal> property be specified when
using this feature</para></listitem>
</itemizedlist>
</para>
</section>
<section id="ref_guide_dbsetup_setDSError">
<title>Error handling</title>
<para>
If a JTA DataSource is not available when the EntityManager is created an
<link linkend=""><literal>ArgumentException</literal></link> will be thrown.
The EntityManager will not fall back on the JTA DataSource defined in the
configuration.
</para>
<para>
The same logic applies if a Non-JTA DataSource is not available when the
EntityManager is created. OpenJPA will not fall back to the configured
non-JTA DataSource.
</para>
</section>
</section>
</section>
</section> </section>
<section id="ref_guide_dbsetup_sqlconn"> <section id="ref_guide_dbsetup_sqlconn">
<title> <title>