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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 2005-04-15 15:43:46 +00:00
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94
reference/en/modules/batch.xml
View File

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

9
reference/en/modules/query_hql.xml
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@ -970,6 +970,15 @@ order by account.type.sortOrder, account.accountNumber, payment.dueDate]]></prog
</sect1>
<sect1 id="queryhql-bulk">
<title>Bulk UPDATE &amp; DELETE Statements</title>
<para>
HQL now supports UPDATE and DELETE statements in HQL. See
<xref linkend="batch-direct"/> for details.
</para>
</sect1>
<sect1 id="queryhql-tipstricks">
<title>Tips &amp; Tricks</title>