Edit File: dpl_replace.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 V1.62.4" /> <link rel="home" href="index.html" title="Getting Started with Berkeley DB" /> <link rel="up" href="persist_access.html" title="Chapter 5. Saving and Retrieving Objects" /> <link rel="previous" href="dpl_delete.html" title="Deleting Entity Objects" /> <link rel="next" href="dpl_example.html" title="Chapter 6. A DPL Example" /> </head> <body> <div class="navheader"> <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></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 <tt class="literal">skeyoneupdated</tt> instead of the previous value, which was <tt class="literal">skeyone</tt> </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 <tt class="classname">EntityCursor</tt>, you can update each object in turn using <tt class="methodname">EntityCursor.update()</tt>. Note, however, that you must be iterating using a <tt class="classname">PrimaryIndex</tt>; this operation is not allowed if you are using a <tt class="classname">SecondaryIndex</tt>. </p> <p> For example, the following iterates over every <tt class="classname">SimpleEntityClass</tt> object in the entity store, and it changes them all so that they have a secondary index of <tt class="literal">updatedskey</tt>: </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>
Back to File Manager