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