Title: DataChannel

	
<P><TT>&quot;org.apache.cayenne.DataChannel&quot;</TT> is an abstraction of Cayenne persistence stack. It is very simple - it defines only 4 methods, two for actually performing persistent operations, one to access metadata, and one - to access EventManager:</P>

<DIV class="code panel" style="border-width: 1px;"><DIV class="codeHeader panelHeader" style="border-bottom-width: 1px;"><B>DataChannel.java</B></DIV><DIV class="codeContent panelContent">
<PRE class="code-java"><SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">interface</SPAN> DataChannel {

    QueryResponse onQuery(ObjectContext originatingContext, Query query);

    GraphDiff onSync(ObjectContext originatingContext, GraphDiff changes, <SPAN class="code-object">int</SPAN> syncType);

    EventManager getEventManager();

    EntityResolver getEntityResolver();
}</PRE>
</DIV></DIV>

<P>DataChannel is rarely used by the application directly. Instead ObjectContexts use it internally as an abstract persistent store. There are few kinds of DataChannels in Cayenne:</P>

<UL>
	<LI>DataDomain (the most commonly used DataChannel) connects to one or more databases via DataNodes.</LI>
	<LI>DataContext can serve as a DataChannel for other DataContexts</LI>
	<LI>ClientChannel is a DataChannel that connects to a remote Cayenne service.</LI>
</UL>