Hibernate SVN: r14917 -  search/trunk/doc...

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Author: hardy.ferentschik
Date: 2008-07-10 11:49:26 -0400 (Thu, 10 Jul 2008)
New Revision: 14917

Modified:
search/trunk/doc/reference/en/modules/query.xml
Log:
HSEARCH-174:
- Updated the filter documentation.

Modified: search/trunk/doc/reference/en/modules/query.xml
===================================================================
--- search/trunk/doc/reference/en/modules/query.xml 2008-07-10 15:16:19 UTC (rev 14916)
+++ search/trunk/doc/reference/en/modules/query.xml 2008-07-10 15:49:26 UTC (rev 14917)
@@(protected) @@
<?xml version="1.0" encoding="UTF-8"?>
-
<chapter id="search-query" xreflabel="Querying">
+ 
+
<title>Querying</title>

<para>The second most important capability of Hibernate Search is the
@@(protected) @@
<section>
<title>Filters</title>

- <para>Apache Lucene has a powerful feature that allows to filters results
- from a query according to a custom filtering process. This is a very
- powerful way to apply some data restrictions after a query, especially
- since filters can be cached and reused. Some interesting usecases
- are:</para>
+ <para>Apache Lucene has a powerful feature that allows to filter query
+ results according to a custom filtering process. This is a very powerful
+ way to apply additional data restrictions, especially since filters can be
+ cached and reused. Some interesting usecases are:</para>

<itemizedlist>
<listitem>
@@(protected) @@
</itemizedlist>

<para>Hibernate Search pushes the concept further by introducing the
- notion of parameterizable named filters which are transparantly cached.
+ notion of parameterizable named filters which are transparently cached.
For people familiar with the notion of Hibernate Core filters, the API is
- very similar.</para>
+ very similar:</para>

<programlisting>fullTextQuery = s.createFullTextQuery( query, Driver.class );
fullTextQuery.enableFullTextFilter("bestDriver");
fullTextQuery.enableFullTextFilter("security").setParameter( "login", "andre" );
fullTextQuery.list(); //returns only best drivers where andre has credentials</programlisting>

- <para>In this example we enabled 2 filters on top of this query. You can
+ <para>In this example we enabled two filters on top of the query. You can
enable (or disable) as many filters as you want.</para>

<para>Declaring filters is done through the
<classname>@(protected)
- be on any <literal>@(protected)
- operation.</para>
+ be on any <literal>@(protected)
+ filter is later applied to. Filter names must be unique since all filters
+ are globally visible. Each named filter has to point to an actual filter
+ implementation.</para>

<programlisting>@(protected)
@Indexed
@@(protected) @@
})
public class Driver { ... }</programlisting>

- <para>Each named filter points to an actual filter implementation.</para>
-
<programlisting>public class BestDriversFilter extends <emphasis
role="bold">org.apache.lucene.search.Filter</emphasis> {

@@(protected) @@
}</programlisting>

<para><classname>BestDriversFilter</classname> is an example of a simple
- Lucene filter that will filter all results to only return drivers whose
- score is 5. The filters must have a no-arg constructor when referenced in
- a <literal>FulltextFilterDef.impl</literal>.</para>
-
- <para>The <literal>cache</literal> flag, defaulted to
+ Lucene filter that will filter all results returning only drivers whose
+ score is 5. In this example the specified filter implements the
+ <literal>org.apache.lucene.search.Filter</literal> directly and contains a
+ no-arg constructor. The <literal>cache</literal> flag, defaulted to
<literal>true</literal>, tells Hibernate Search to search the filter in
- its internal cache and reuses it if found.</para>
+ its internal cache and reuse it if found.</para>

- <para>Note that, usually, filter using the
- <classname>IndexReader</classname> are wrapped in a Lucene
- <classname>CachingWrapperFilter</classname> to benefit from some caching
- speed improvement. If your Filter creation requires additional steps or if
- the filter you are willing to use does not have a no-arg constructor, you
- can use the factory pattern:</para>
+ <para>If your Filter creation requires additional steps or if the filter
+ you want to use does not have a no-arg constructor, you can use the
+ factory pattern:</para>

<programlisting>@(protected)
@Indexed
@@(protected) @@
similar to the component factory pattern, but the annotation is
different!</para>

- <para>Named filters comes in handy where the filters have parameters. For
- example a security filter needs to know which credentials you are willing
- to filter by:</para>
+ <para>Named filters come in handy where parameters have to be passed to
+ the filter. For example a security filter might want to know which
+ security level you want to apply:</para>

<programlisting>fullTextQuery = s.createFullTextQuery( query, Driver.class );
fullTextQuery.enableFullTextFilter("security")<emphasis role="bold">.setParameter( "level", 5 )</emphasis>;</programlisting>
@@(protected) @@
}
}</programlisting>

- <para>Note the method annotated <classname>@(protected)
- a <classname>FilterKey</classname> object. The returned object has a
- special contract: the key object must implement equals / hashcode so that
- 2 keys are equals if and only if the given Filter types are the same and
- the set of parameters are the same. In other words, 2 filter keys are
- equal if and only if the filters from which the keys are generated can be
- interchanged. The key object is used as a key in the cache
- mechanism.</para>
+ <para>Note the method annotated <classname>@(protected)
+ <classname>FilterKey</classname> object. The returned object has a special
+ contract: the key object must implement equals / hashcode so that 2 keys
+ are equal if and only if the given <classname>Filter</classname> types are
+ the same and the set of parameters are the same. In other words, 2 filter
+ keys are equal if and only if the filters from which the keys are
+ generated can be interchanged. The key object is used as a key in the
+ cache mechanism.</para>

<para><classname>@(protected)>

@@(protected) @@
</itemizedlist>

<para>In most cases, using the <literal>StandardFilterKey</literal>
- implementation will be good enough. It delegates the equals/hashcode
+ implementation will be good enough. It delegates the equals / hashcode
implementation to each of the parameters equals and hashcode
methods.</para>

- <para>Why should filters be cached? There are two area where filter
- caching shines:</para>
+ <para>The filter cache is enabled by default and uses the notion of
+ SoftReferences to dispose memory when needed. To adjust the size of the
+ hard reference cache, use
+ <literal>hibernate.search.filter.cache_strategy.size</literal> (defaults
+ to 128). For advance use of filter caching, you can implement your own
+ <classname>FilterCachingStrategy</classname>. The classname is defined by
+ <literal>hibernate.search.filter.cache_strategy</literal>.</para>

+ <para>The described filter cache should not be confused with caching the
+ actual filter results. In Lucene it is common practise to wrap filters
+ using the <classname>IndexReader</classname> around a
+ <classname>CachingWrapperFilter.</classname> The wrapper will cache the
+ <classname>BitSet</classname> returned from the
+ <methodname>bits(IndexReader reader)</methodname>method to avoid expensive
+ recomputation. </para>
+
+ <para>Hibernate Search also takes care of this aspect of caching. If the
+ <literal>cache</literal> flag of <classname>@(protected)
+ </classname>is set to <literal>true</literal>, it will automatically wrap
+ the specified filter around a Hibernate specific implementation of
+ CachingWrapperFilter
+ (<classname>org.hibernate.search.filter.CachingWrapperFilter</classname>).
+ In contrast to Lucene's version of this class SoftReferences are used
+ together with a hard reference count. The hard reference count can be
+ adjusted using
+ <literal>hibernate.search.filter.caching_wrapper.size</literal> (defaults
+ to 5). The wrapping behaviour can be controlled by
+ <literal>@(protected)
+ three differerent values for this parameter:</para>
+
+ <para><informaltable align="left" width="">
+ <tgroup cols="2">
+ <colspec align="center" />
+
+ <thead>
+ <row>
+ <entry align="center">Value</entry>
+
+ <entry align="center">Definition</entry>
+ </row>
+ </thead>
+
+ <tbody>
+ <row>
+ <entry align="left">CacheBitSet.AUTOMATIC</entry>
+
+ <entry>The use of <classname>CachingWrapperFilter</classname>
+ depends on the <literal>cache</literal> paramter of the filter
+ defintion. If <literal>cache</literal> is set to
+ <literal>true</literal> a wrapper will be used, otherwise not.
+ <literal>CacheBitSet.AUTOMATIC</literal> is the default
+ value.</entry>
+ </row>
+
+ <row>
+ <entry align="left">CacheBitSet.NO</entry>
+
+ <entry>No wrapper will be used.</entry>
+ </row>
+
+ <row>
+ <entry align="left">CacheBitSet.YES</entry>
+
+ <entry>The specified filter will be wrapped independent of the
+ <literal>cache</literal> flag. (Note, this options is quite
+ meaningless, because even though the BitSet will be cached there
+ is currently no way to reuse the fitler.)</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>Last but not least - why should filters be cached? There
+ are two areas where filter caching shines:</para>
+
<itemizedlist>
<listitem>
<para>the system does not update the targeted entity index often (in
@@(protected) @@
spent to execute the query)</para>
</listitem>
</itemizedlist>
-
- <para>Cache is enabled by default and use the notion of SoftReferences to
- dispose memory when needed. To adjust the size of the hard reference
- cache, use <literal>hibernate.search.filter.cache_strategy.size</literal>
- (defaults to 128). Don't forget to use a
- <classname>CachingWrapperFilter</classname> when the filter is cacheable
- and the Filter's bits methods makes use of IndexReader.</para>
-
- <para>For advance use of filter caching, you can implement your own
- <classname>FilterCachingStrategy</classname>. The classname is defined by
- <literal>hibernate.search.filter.cache_strategy</literal>.</para>
</section>

<section>

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