mirror of
https://github.com/berkeleydb/je.git
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156 lines
5.7 KiB
HTML
156 lines
5.7 KiB
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>Using Secondary 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 V1.73.2" />
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<link rel="start" href="index.html" title="Getting Started with Berkeley DB Java Edition" />
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<link rel="up" href="indexes.html" title="Chapter 10. Secondary Databases" />
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<link rel="prev" href="secondaryDelete.html" title="Deleting Secondary Database Records" />
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<link rel="next" href="joins.html" title="Database Joins" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 12.2.7.5</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">
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<span xmlns="http://www.w3.org/1999/xhtml">Using Secondary Cursors</span>
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</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="secondaryDelete.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 10. Secondary Databases</th>
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<td width="20%" align="right"> <a accesskey="n" href="joins.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="secondaryCursor"></a>
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<span>Using Secondary Cursors</span>
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</h2>
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</div>
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</div>
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</div>
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<p>
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Just like cursors on a primary database, you can use
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<span>secondary cursors</span>
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to iterate over the records in a secondary database. Like
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<span>normal cursors,</span>
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you can also use
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<span>secondary cursors</span>
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to search for specific records in a database, to seek to the first
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or last record in the database, to get the next duplicate record,
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<span>to get the next non-duplicate record,</span>
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and so forth. For a complete description on cursors and their capabilities, see
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<a class="xref" href="Cursors.html" title="Chapter 9. Using Cursors">Using Cursors</a>.
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</p>
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<p>
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However, when you use
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<span>secondary cursors:</span>
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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Any data returned is the data contained on the primary database
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record referenced by the secondary record.
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</p>
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</li>
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<li>
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<p>
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<code class="methodname">SecondaryCursor.getSearchBoth()</code> and
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related methods do not search based on a key/data pair. Instead, you
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search based on a secondary key and a primary key. The data returned
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is the primary data that most closely matches the two keys provided
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for the search.
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</p>
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</li>
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</ul>
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</div>
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<p>
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For example, suppose you are using the databases, classes, and key
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<span>creators</span>
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described in <a class="xref" href="keyCreator.html" title="Implementing Key Creators">Implementing Key
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<span>Creators</span>
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</a>.
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Then the following searches for a person's
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name in the secondary database, and deletes all secondary and primary
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records that use that name.
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</p>
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<a id="je_index8"></a>
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<pre class="programlisting">package je.gettingStarted;
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import com.sleepycat.je.DatabaseEntry;
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import com.sleepycat.je.LockMode;
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import com.sleepycat.je.OperationStatus;
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import com.sleepycat.je.SecondaryDatabase;
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import com.sleepycat.je.SecondaryCursor;
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...
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try {
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// Database and environment opens omitted for brevity
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...
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String secondaryName = "John Doe";
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DatabaseEntry secondaryKey =
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new DatabaseEntry(secondaryName.getBytes("UTF-8"));
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DatabaseEntry foundData = new DatabaseEntry();
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SecondaryCursor mySecCursor =
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mySecondaryDatabase.openSecondaryCursor(null, null);
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OperationStatus retVal = mySecCursor.getSearchKey(secondaryKey,
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foundData,
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LockMode.DEFAULT);
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while (retVal == OperationStatus.SUCCESS) {
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mySecCursor.delete();
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retVal = mySecCursor.getNextDup(secondaryKey,
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foundData,
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LockMode.DEFAULT);
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}
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} catch (Exception e) {
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// Exception handling goes here
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}</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="secondaryDelete.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="indexes.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="joins.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 Secondary Database Records </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"> Database Joins</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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