Import BSDDB 4.7.25 (as of svn r89086)
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Zachary Ware
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docs/gsg/JAVA/ReplacingEntryWCursor.html
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132
docs/gsg/JAVA/ReplacingEntryWCursor.html
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<?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 Records Using Cursors</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="Cursors.html" title="Chapter 9. Using Cursors" />
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<link rel="previous" href="DeleteEntryWCursor.html" title="Deleting Records Using Cursors" />
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<link rel="next" href="cursorJavaUsage.html" title="Cursor 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 Records Using Cursors</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="DeleteEntryWCursor.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 9. Using Cursors</th>
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<td width="20%" align="right"> <a accesskey="n" href="cursorJavaUsage.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="ReplacingEntryWCursor"></a>Replacing Records Using Cursors</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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You replace the data for a database record by using
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<span>
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<tt class="methodname">Cursor.putCurrent()</tt>.
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</span>
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</p>
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<a id="java_cursor9"></a>
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<pre class="programlisting">import com.sleepycat.db.Cursor;
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import com.sleepycat.db.Database;
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import com.sleepycat.db.DatabaseEntry;
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import com.sleepycat.db.LockMode;
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import com.sleepycat.db.OperationStatus;
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...
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Cursor cursor = null;
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Database myDatabase = null;
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try {
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...
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// Database open omitted for brevity
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...
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// Create DatabaseEntry objects
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// searchKey is some String.
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DatabaseEntry theKey = new DatabaseEntry(searchKey.getBytes("UTF-8"));
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DatabaseEntry theData = new DatabaseEntry();
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// Open a cursor using a database handle
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cursor = myDatabase.openCursor(null, null);
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// Position the cursor. Ignoring the return value for clarity
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OperationStatus retVal = cursor.getSearchKey(theKey, theData,
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LockMode.DEFAULT);
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// Replacement data
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String replaceStr = "My replacement string";
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DatabaseEntry replacementData =
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new DatabaseEntry(replaceStr.getBytes("UTF-8"));
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cursor.putCurrent(replacementData);
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} catch (Exception e) {
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// Exception handling goes here
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} finally {
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// Make sure to close the cursor
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cursor.close();
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}</pre>
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<p>
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Note that you cannot change a record's key using this method; the key
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parameter is always ignored when you replace a record.
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</p>
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<p>
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When replacing the data portion of a record, if you are replacing a
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record that is a member of a sorted duplicates set, then the replacement
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will be successful only if the new record sorts identically to the old
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record. This means that if you are replacing a record that is a member
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of a sorted duplicates set, and if you are using the default
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lexicographic sort, then the replacement will fail due to violating the
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sort order. However, if you
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provide a custom sort routine that, for example, sorts based on just a
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few bytes out of the data item, then potentially you can perform
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a direct replacement and still not violate the restrictions described
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here.
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</p>
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<p>
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<span>Under these circumstances, if</span>
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you want to replace the data contained by a duplicate record,
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<span>
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and you are not using a custom sort routine, then
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</span>
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delete the record and create a new record with the desired key and data.
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</p>
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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="DeleteEntryWCursor.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="Cursors.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="cursorJavaUsage.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 Records Using Cursors </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"> Cursor 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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