added doc on bulk UPDATE/DELETE statements
git-svn-id: https://svn.jboss.org/repos/hibernate/trunk/Hibernate3/doc@6430 1b8cb986-b30d-0410-93ca-fae66ebed9b2
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Steve Ebersole
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@ -95,4 +95,98 @@ session.close();]]></programlisting>
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</sect1>
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</sect1>
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<sect1 id="batch-direct">
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<title>Bulk update/delete</title>
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<para>
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As already discussed, automatic and transparent object/relational mapping is concerned
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with the management of object state. This implies that the object state is available
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in memory, hence updating or deleting (using SQL <literal>UPDATE</literal> and
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<literal>DELETE</literal>) data directly in the database will not affect in-memory
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state. However, Hibernate provides methods for bulk SQL-style <literal>UPDATE</literal>
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and <literal>DELETE</literal> statement execution which are performed through the
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Hibernate Query Language (<xref linkend="queryhql">HQL</xref>).
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</para>
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<para>
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The psuedo-syntax for <literal>UPDATE</literal> and <literal>DELETE</literal> statements
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is: <literal>( UPDATE | DELETE ) FROM? ClassName (WHERE WHERE_CONDITIONS)?</literal>. Some
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points to note:
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</para>
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<itemizedlist spacing="compact">
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<listitem>
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<para>
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In the from-clause, the FROM keyword is optional
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</para>
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</listitem>
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<listitem>
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<para>
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There can only be a single class named in the from-clause, and it <emphasis>cannot</emphasis>
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have an alias.
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</para>
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</listitem>
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<listitem>
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<para>
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No joins (either implicit or explicit) can be specified in a bulk HQL query. Sub-queries
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may be used in the where-clause.
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</para>
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</listitem>
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<listitem>
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<para>
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The where-clause is also optional.
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</para>
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</listitem>
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</itemizedlist>
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<para>
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As an example, to execute an HQL <literal>UPDATE</literal>, use the
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<literal>Query.executeUpdate()</literal> method:
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</para>
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<programlisting><![CDATA[Session session = sessionFactory.openSession();
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Transaction tx = session.beginTransaction();
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String hqlUpdate = "update Customer set name = :newName where name = :oldName";
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int updatedEntities = s.createQuery( hqlUpdate )
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.setString( "newName", newName )
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.setString( "oldName", oldName )
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.executeUpdate();
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tx.commit();
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session.close();]]></programlisting>
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<para>
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To execute an HQL <literal>DELETE</literal>, use the same <literal>Query.executeUpdate()</literal>
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method (the method is named for those familiar with JDBC's
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<literal>PreparedStatement.executeUpdate()</literal>):
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</para>
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<programlisting><![CDATA[Session session = sessionFactory.openSession();
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Transaction tx = session.beginTransaction();
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String hqlDelete = "delete Customer where name = :oldName";
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int deletedEntities = s.createQuery( hqlDelete )
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.setString( "oldName", oldName )
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.executeUpdate();
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tx.commit();
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session.close();]]></programlisting>
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<para>
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The <literal>int</literal> value returned by the <literal>Query.executeUpdate()</literal>
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method indicate the number of entities effected by the operation. Consider this may or may not
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correlate to the number of rows effected in the database. An HQL bulk operation might result in
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multiple actual SQL statements being executed, for joined-subclass, for example. The returned
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number indicates the number of actual entities affected by the statement. Going back to the
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example of joined-subclass, a delete against one of the subclasses may actually result
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in deletes against not just the table to which that subclass is mapped, but also the "root"
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table and potentially joined-subclass tables further down the inheritence hierarchy.
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</para>
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<para>
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Note that there are currently a few limitations with the bulk HQL operations which
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will be addressed in future releases; consult the JIRA roadmap for details.
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</para>
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</sect1>
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</chapter>
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</chapter>
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@ -968,6 +968,15 @@ where :currentUser = user
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and PaymentStatus.UNPAID = isNull(payment.currentStatus.name, PaymentStatus.UNPAID)
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and PaymentStatus.UNPAID = isNull(payment.currentStatus.name, PaymentStatus.UNPAID)
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order by account.type.sortOrder, account.accountNumber, payment.dueDate]]></programlisting>
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order by account.type.sortOrder, account.accountNumber, payment.dueDate]]></programlisting>
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</sect1>
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<sect1 id="queryhql-bulk">
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<title>Bulk UPDATE & DELETE Statements</title>
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<para>
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HQL now supports UPDATE and DELETE statements in HQL. See
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<xref linkend="batch-direct"/> for details.
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</para>
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</sect1>
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</sect1>
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<sect1 id="queryhql-tipstricks">
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<sect1 id="queryhql-tipstricks">
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