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HHH-4006 - Document fetch profiles 

git-svn-id: https://svn.jboss.org/repos/hibernate/core/trunk@17915 1b8cb986-b30d-0410-93ca-fae66ebed9b2
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Steve Ebersole 2009-11-04 22:28:47 +00:00
parent 07ae68ff98
commit 9b8b82b549
1 changed files with 70 additions and 2 deletions
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documentation/manual/src/main/docbook/en-US/content/performance.xml
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@ -589,7 +589,76 @@ Cat fritz = (Cat) iter.next();]]></programlisting>
<!-- TODO: Write more about this -->
</sect2>
<sect2 id="performance-fetching-profiles">
<title>Fetch profiles</title>
<para>
Another way to affect the fetching strategy for loading associated objects is through something
called a fetch profile, which is a named configuration associated with the
<interfacename>org.hibernate.SessionFactory</interfacename> but enabled, by name, on the
<interfacename>org.hibernate.Session</interfacename>. Once enabled on a
<interfacename>org.hibernate.Session</interfacename>, the fetch profile wull be in affect for
that <interfacename>org.hibernate.Session</interfacename> until it is explicitly disabled.
</para>
<para>
So what does that mean? Well lets explain that by way of an example. Say we have
the following mappings:
</para>
<programlisting><![CDATA[<hibernate-mapping>
<class name="Customer">
...
<set name="orders" inverse="true">
<key column="cust_id"/>
<one-to-many class="Order"/>
</set>
</class>
<class name="Order">
...
</class>
</hibernate-mapping>]]></programlisting>
<para>
Now normally when you get a reference to a particular customer, that customer's set of
orders will be lazy meaning we will not yet have loaded those orders from the database.
Normally this is a good thing. Now lets say that you have a certain use case where
it is more efficient to load the customer and their orders together. One way certainly is
to use "dynamic fetching" strategies via an HQL or criteria queries. But another option is
to use a fetch profile to achieve that. Just add the following to your mapping:
</para>
<programlisting><![CDATA[<hibernate-mapping>
...
<fetch-profile name="customer-with-orders">
<fetch entity="Customer" association="orders" style="join"/>
</fetch-profile>
</hibernate-mapping>]]></programlisting>
<para>
or even:
</para>
<programlisting><![CDATA[<hibernate-mapping>
<class name="Customer">
...
<fetch-profile name="customer-with-orders">
<fetch association="orders" style="join"/>
</fetch-profile>
</class>
...
</hibernate-mapping>]]></programlisting>
<para>
Now the following code will actually load both the customer <emphasis>and their orders</emphasis>:
</para>
<programlisting><![CDATA[
Session session = ...;
session.enableFetchProfile( "customer-with-orders" ); // name matches from mapping
Customer customer = (Customer) session.get( Customer.class, customerId );
]]></programlisting>
<para>
Currently only join style fetch profiles are supported, but they plan is to support additional
styles. See <ulink url="http://opensource.atlassian.com/projects/hibernate/browse/HHH-3414">HHH-3414</ulink>
for details.
</para>
</sect2>
<sect2 id="performance-fetching-lazyproperties">
<title>Using lazy property fetching</title>
@ -653,7 +722,6 @@ Cat fritz = (Cat) iter.next();]]></programlisting>
</para>
</sect2>
</sect1>
<sect1 id="performance-cache" revision="1">