mirror of
https://github.com/berkeleydb/je.git
synced 2024-11-20 11:16:25 +00:00
110 lines
4.8 KiB
HTML
110 lines
4.8 KiB
HTML
|
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
|
|||
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
|||
|
|
<html xmlns="http://www.w3.org/1999/xhtml">
|
|||
|
|
<head>
|
|||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
|
|||
|
|
<title>Replacing Entity Objects</title>
|
|||
|
|
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
|
|||
|
|
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
|
|||
|
|
<link rel="start" href="index.html" title="Getting Started with Berkeley DB Java Edition" />
|
|||
|
|
<link rel="up" href="persist_access.html" title="Chapter 5. Saving and Retrieving Objects" />
|
|||
|
|
<link rel="prev" href="dpl_delete.html" title="Deleting Entity Objects" />
|
|||
|
|
<link rel="next" href="dpl_example.html" title="Chapter 6. A DPL Example" />
|
|||
|
|
</head>
|
|||
|
|
<body>
|
|||
|
|
<div xmlns="" class="navheader">
|
|||
|
|
<div class="libver">
|
|||
|
|
<p>Library Version 12.2.7.5</p>
|
|||
|
|
</div>
|
|||
|
|
<table width="100%" summary="Navigation header">
|
|||
|
|
<tr>
|
|||
|
|
<th colspan="3" align="center">Replacing Entity Objects</th>
|
|||
|
|
</tr>
|
|||
|
|
<tr>
|
|||
|
|
<td width="20%" align="left"><a accesskey="p" href="dpl_delete.html">Prev</a> </td>
|
|||
|
|
<th width="60%" align="center">Chapter 5. Saving and Retrieving Objects</th>
|
|||
|
|
<td width="20%" align="right"> <a accesskey="n" href="dpl_example.html">Next</a></td>
|
|||
|
|
</tr>
|
|||
|
|
</table>
|
|||
|
|
<hr />
|
|||
|
|
</div>
|
|||
|
|
<div class="sect1" lang="en" xml:lang="en">
|
|||
|
|
<div class="titlepage">
|
|||
|
|
<div>
|
|||
|
|
<div>
|
|||
|
|
<h2 class="title" style="clear: both"><a id="dpl_replace"></a>Replacing Entity Objects</h2>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
<p>
|
|||
|
|
To modify a stored entity object, retrieve it, update
|
|||
|
|
it, then put it back to the entity store:
|
|||
|
|
</p>
|
|||
|
|
<pre class="programlisting">
|
|||
|
|
SimpleEntityClass sec = sda.pIdx.get("keyone");
|
|||
|
|
sec.setSKey("skeyoneupdated");
|
|||
|
|
sda.pIdx.put(sec);
|
|||
|
|
</pre>
|
|||
|
|
<p>
|
|||
|
|
Note that because we updated a field on the object that is
|
|||
|
|
a secondary key, this object will now be accessible by the
|
|||
|
|
secondary key of <code class="literal">skeyoneupdated</code> instead
|
|||
|
|
of the previous value, which was <code class="literal">skeyone</code>
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
Be aware that if you modify the object's primary key, the behavior is
|
|||
|
|
somewhat different. In this case, you cause a new instance
|
|||
|
|
of the object to be created in the store, instead of
|
|||
|
|
replacing an existing instance:
|
|||
|
|
</p>
|
|||
|
|
<pre class="programlisting">// Results in two objects in the store. One with a
|
|||
|
|
// primary index of "keyfive" and the other with primary index of
|
|||
|
|
//'keyfivenew'.
|
|||
|
|
SimpleEntityClass sec = sda.pIdx.get("keyfive");
|
|||
|
|
sec.setPKey("keyfivenew");
|
|||
|
|
sda.pIdx.put(sec); </pre>
|
|||
|
|
<p>
|
|||
|
|
Finally, if you are iterating over a collection of objects
|
|||
|
|
using an <code class="classname">EntityCursor</code>, you can
|
|||
|
|
update each object in turn using
|
|||
|
|
<code class="methodname">EntityCursor.update()</code>. Note,
|
|||
|
|
however, that you must be iterating using a
|
|||
|
|
<code class="classname">PrimaryIndex</code>; this operation is not
|
|||
|
|
allowed if you are using a
|
|||
|
|
<code class="classname">SecondaryIndex</code>.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
For example, the following iterates over every
|
|||
|
|
<code class="classname">SimpleEntityClass</code> object in the entity
|
|||
|
|
store, and it changes them all so that they have a
|
|||
|
|
secondary index of <code class="literal">updatedskey</code>:
|
|||
|
|
</p>
|
|||
|
|
<pre class="programlisting">EntityCursor<SimpleEntityClass> sec_pcursor = sda.pIdx.entities();
|
|||
|
|
for (SimpleEntityClass sec : sec_pcursor) {
|
|||
|
|
sec.setSKey("updatedskey");
|
|||
|
|
sec_pcursor.update(item);
|
|||
|
|
}
|
|||
|
|
sec_pcursor.close(); </pre>
|
|||
|
|
</div>
|
|||
|
|
<div class="navfooter">
|
|||
|
|
<hr />
|
|||
|
|
<table width="100%" summary="Navigation footer">
|
|||
|
|
<tr>
|
|||
|
|
<td width="40%" align="left"><a accesskey="p" href="dpl_delete.html">Prev</a> </td>
|
|||
|
|
<td width="20%" align="center">
|
|||
|
|
<a accesskey="u" href="persist_access.html">Up</a>
|
|||
|
|
</td>
|
|||
|
|
<td width="40%" align="right"> <a accesskey="n" href="dpl_example.html">Next</a></td>
|
|||
|
|
</tr>
|
|||
|
|
<tr>
|
|||
|
|
<td width="40%" align="left" valign="top">Deleting Entity Objects </td>
|
|||
|
|
<td width="20%" align="center">
|
|||
|
|
<a accesskey="h" href="index.html">Home</a>
|
|||
|
|
</td>
|
|||
|
|
<td width="40%" align="right" valign="top"> Chapter 6. A DPL Example</td>
|
|||
|
|
</tr>
|
|||
|
|
</table>
|
|||
|
|
</div>
|
|||
|
|
</body>
|
|||
|
|
</html>
|