1<?xml version="1.0" encoding="UTF-8" standalone="no"?>
2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
3<html xmlns="http://www.w3.org/1999/xhtml">
4  <head>
5    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
6    <title>Replacing Entity Objects</title>
7    <link rel="stylesheet" href="gettingStarted.css" type="text/css" />
8    <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
9    <link rel="start" href="index.html" title="Getting Started with Berkeley DB" />
10    <link rel="up" href="persist_access.html" title="Chapter��5.��Saving and Retrieving Objects" />
11    <link rel="prev" href="dpl_delete.html" title="Deleting Entity Objects" />
12    <link rel="next" href="dpl_example.html" title="Chapter��6.��A DPL Example" />
13  </head>
14  <body>
15    <div class="navheader">
16      <table width="100%" summary="Navigation header">
17        <tr>
18          <th colspan="3" align="center">Replacing Entity Objects</th>
19        </tr>
20        <tr>
21          <td width="20%" align="left"><a accesskey="p" href="dpl_delete.html">Prev</a>��</td>
22          <th width="60%" align="center">Chapter��5.��Saving and Retrieving Objects</th>
23          <td width="20%" align="right">��<a accesskey="n" href="dpl_example.html">Next</a></td>
24        </tr>
25      </table>
26      <hr />
27    </div>
28    <div class="sect1" lang="en" xml:lang="en">
29      <div class="titlepage">
30        <div>
31          <div>
32            <h2 class="title" style="clear: both"><a id="dpl_replace"></a>Replacing Entity Objects</h2>
33          </div>
34        </div>
35      </div>
36      <p>
37                   To modify a stored entity object, retrieve it, update
38                   it, then put it back to the entity store:
39           </p>
40      <pre class="programlisting">
41SimpleEntityClass sec = sda.pIdx.get("keyone");
42sec.setSKey("skeyoneupdated");
43sda.pIdx.put(sec);
44</pre>
45      <p>
46                Note that because we updated a field on the object that is
47                a secondary key, this object will now be accessible by the
48                secondary key of <code class="literal">skeyoneupdated</code> instead
49                of the previous value, which was <code class="literal">skeyone</code>
50        </p>
51      <p>
52                Be aware that if you modify the object's primary key, the behavior is
53                somewhat different. In this case, you cause a new instance
54                of the object to be created in the store, instead of
55                replacing an existing instance:
56        </p>
57      <pre class="programlisting">// Results in two objects in the store.  One with a
58// primary index of "keyfive" and the other with primary index of 
59//'keyfivenew'.
60SimpleEntityClass sec = sda.pIdx.get("keyfive");
61sec.setPKey("keyfivenew");
62sda.pIdx.put(sec); </pre>
63      <p>
64                Finally, if you are iterating over a collection of objects
65                using an <code class="classname">EntityCursor</code>, you can
66                update each object in turn using
67                <code class="methodname">EntityCursor.update()</code>. Note,
68                however, that you must be iterating using a
69                <code class="classname">PrimaryIndex</code>; this operation is not
70                allowed if you are using a
71                <code class="classname">SecondaryIndex</code>.
72        </p>
73      <p>
74                For example, the following iterates over every
75                <code class="classname">SimpleEntityClass</code> object in the entity
76                store, and it changes them all so that they have a
77                secondary index of <code class="literal">updatedskey</code>:
78        </p>
79      <pre class="programlisting">EntityCursor&lt;SimpleEntityClass&gt; sec_pcursor = sda.pIdx.entities();
80for (SimpleEntityClass sec : sec_pcursor) {
81    sec.setSKey("updatedskey");
82    sec_pcursor.update(item);
83}
84sec_pcursor.close(); </pre>
85    </div>
86    <div class="navfooter">
87      <hr />
88      <table width="100%" summary="Navigation footer">
89        <tr>
90          <td width="40%" align="left"><a accesskey="p" href="dpl_delete.html">Prev</a>��</td>
91          <td width="20%" align="center">
92            <a accesskey="u" href="persist_access.html">Up</a>
93          </td>
94          <td width="40%" align="right">��<a accesskey="n" href="dpl_example.html">Next</a></td>
95        </tr>
96        <tr>
97          <td width="40%" align="left" valign="top">Deleting Entity Objects��</td>
98          <td width="20%" align="center">
99            <a accesskey="h" href="index.html">Home</a>
100          </td>
101          <td width="40%" align="right" valign="top">��Chapter��6.��A DPL Example</td>
102        </tr>
103      </table>
104    </div>
105  </body>
106</html>
107