minor changes to collections

git-svn-id: https://svn.jboss.org/repos/hibernate/trunk/Hibernate3/doc@4413 1b8cb986-b30d-0410-93ca-fae66ebed9b2

reference/en/modules/collection_mapping.xml

@@ -572,10 +572,11 @@ kittens = cat.getKittens(); //Okay, kittens collection is a Set
         <para>
             Collections (other than arrays) may be lazily initialized, meaning they load
             their state from the database only when the application needs to access it.
-            Initialization happens transparently to the user so the application would not
-            normally need to worry about this (in fact, transparent lazy initialization is
-            the main reason why Hibernate needs its own collection implementations).
-            However, if the application tries something like this:
+            Initialization of collections owned by persistent instances happens transparently 
+            to the user, so the application would not normally need to worry about this (in 
+            fact, transparent lazy initialization is the main reason why Hibernate needs its 
+            own collection implementations). However, if the application tries something like 
+            this:
         </para>
 
         <programlisting><![CDATA[s = sessions.openSession();
@@ -588,17 +589,20 @@ Integer accessLevel = (Integer) permissions.get("accounts");  // Error!]]></prog
 
         <para>
             It could be in for a nasty surprise. Since the permissions collection was not
-            initialized when the <literal>Session</literal> was committed,
-            the collection will never be able to load its state. The fix is to move the
+            initialized when the <literal>Session</literal> was closed, the collection 
+            will not be able to load its state. <emphasis>Hibernate does not support lazy
+            initialization for detached objects</emphasis>. The fix is to move the
             line that reads from the collection to just before the commit. (There are
             other more advanced ways to solve this problem, however.)
         </para>
 
         <para>
-            Alternatively, use a non-lazy collection. Since lazy initialization can lead to
+            It's possible to use a non-lazy collection. Since lazy initialization can lead to
             bugs like that above, non-laziness is the default. However, it is intended that
-            lazy initialization be used for almost all collections, especially for
-            collections of entities (for reasons of efficiency).
+            lazy initialization be used for almost all collections, especially for collections 
+            of entities (for reasons of efficiency). If you define too many non-lazy associations
+            in your object model, Hibernate will end up needing to fetch the entire database
+            into memory in every transaction!
         </para>
 
         <para>
@@ -662,16 +666,15 @@ Integer accessLevel = (Integer) permissions.get("accounts");  // Error!]]></prog
         </itemizedlist>
 
         <para>
-            You can use the <literal>filter()</literal> method of the Hibernate Session API to
-            get the size of a collection without initializing it:
+            You can use a collection filter to get the size of a collection without initializing it:
         </para>
 
-        <programlisting><![CDATA[( (Integer) s.filter( collection, "select count(*)" ).get(0) ).intValue()]]></programlisting>
+        <programlisting><![CDATA[( (Integer) s.createFilter( collection, "select count(*)" ).list().get(0) ).intValue()]]></programlisting>
 
         <para>
-            <literal>filter()</literal> or <literal>createFilter()</literal> are also used to
-            efficiently retrieve subsets of a collection without needing to initialize the whole
-            collection.
+            The <literal>createFilter()</literal> method is also used to efficiently retrieve subsets
+            of a collection without needing to initialize the whole collection. (And the new 
+            <literal>&lt;filter&gt;</literal> functionality is a more powerful approach.)
         </para>
 
     </sect1>
@@ -905,9 +908,9 @@ session.update(category);                 // The relationship will be saved]]></
         <title>Ternary Associations</title>
 
         <para>
-            There are two possible approaches to mapping a ternary association. One approach is to use
-            composite elements (discussed below). Another is to use a <literal>Map</literal> with an
-            association as its index:
+            There are three possible approaches to mapping a ternary association. One approach 
+            is to use composite elements (discussed below). Another is to use a <literal>Map</literal> 
+            with an association as its index:
         </para>
 
         <programlisting><![CDATA[<map name="contracts" lazy="true">
@@ -922,6 +925,11 @@ session.update(category);                 // The relationship will be saved]]></
     <many-to-many column="connection_id" class="Connection"/>
 </map>]]></programlisting>
             
+        <para>
+            A final alternative is to simply remodel the association as an entity class. This
+            is the approach we use most commonly.
+        </para>
+        
 	</sect1>
 	
 	<sect1 id="collections-heterogeneous">