| Title: DataChannel |
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| <P><TT>"org.apache.cayenne.DataChannel"</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> |
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| <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 { |
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| QueryResponse onQuery(ObjectContext originatingContext, Query query); |
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| GraphDiff onSync(ObjectContext originatingContext, GraphDiff changes, <SPAN class="code-object">int</SPAN> syncType); |
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| EventManager getEventManager(); |
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| EntityResolver getEntityResolver(); |
| }</PRE> |
| </DIV></DIV> |
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| <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> |
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| <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> |
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