108 lines
4.6 KiB
HTML
108 lines
4.6 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Replacing Entity Objects</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.62.4" />
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<link rel="home" href="index.html" title="Getting Started with Berkeley DB" />
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<link rel="up" href="persist_access.html" title="Chapter 5. Saving and Retrieving Objects" />
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<link rel="previous" href="dpl_delete.html" title="Deleting Entity Objects" />
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<link rel="next" href="dpl_example.html" title="Chapter 6. A DPL Example" />
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</head>
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<body>
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<div class="navheader">
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Replacing Entity Objects</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dpl_delete.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 5. Saving and Retrieving Objects</th>
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<td width="20%" align="right"> <a accesskey="n" href="dpl_example.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="dpl_replace"></a>Replacing Entity Objects</h2>
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</div>
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</div>
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<div></div>
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</div>
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<p>
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To modify a stored entity object, retrieve it, update
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it, then put it back to the entity store:
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</p>
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<pre class="programlisting">
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SimpleEntityClass sec = sda.pIdx.get("keyone");
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sec.setsKey("skeyoneupdated");
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sda.pIdx.put(sec);
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</pre>
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<p>
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Note that because we updated a field on the object that is
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a secondary key, this object will now be accessible by the
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secondary key of <tt class="literal">skeyoneupdated</tt> instead
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of the previous value, which was <tt class="literal">skeyone</tt>
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</p>
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<p>
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Be aware that if you modify the object's primary key, the behavior is
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somewhat different. In this case, you cause a new instance
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of the object to be created in the store, instead of
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replacing an existing instance:
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</p>
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<pre class="programlisting">// Results in two objects in the store. One with a
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// primary index of "keyfive" and the other with primary index of
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//'keyfivenew'.
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SimpleEntityClass sec = sda.pIdx.get("keyfive");
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sec.setpKey("keyfivenew");
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sda.pIdx.put(sec); </pre>
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<p>
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Finally, if you are iterating over a collection of objects
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using an <tt class="classname">EntityCursor</tt>, you can
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update each object in turn using
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<tt class="methodname">EntityCursor.update()</tt>. Note,
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however, that you must be iterating using a
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<tt class="classname">PrimaryIndex</tt>; this operation is not
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allowed if you are using a
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<tt class="classname">SecondaryIndex</tt>.
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</p>
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<p>
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For example, the following iterates over every
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<tt class="classname">SimpleEntityClass</tt> object in the entity
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store, and it changes them all so that they have a
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secondary index of <tt class="literal">updatedskey</tt>:
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</p>
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<pre class="programlisting">EntityCursor<SimpleEntityClass> sec_pcursor = sda.pIdx.entities();
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for (SimpleEntityClass sec : sec_pcursor) {
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sec.setsKey("updatedskey");
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sec_pcursor.update(item);
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}
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sec_pcursor.close(); </pre>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="dpl_delete.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="persist_access.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="dpl_example.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Deleting Entity Objects </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Chapter 6. A DPL Example</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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