mirror of
https://github.com/berkeleydb/je.git
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126 lines
5 KiB
HTML
126 lines
5 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>Reading Secondary Databases</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="secondaryProps.html" title="Secondary Database Properties" />
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<link rel="next" href="secondaryDelete.html" title="Deleting Secondary Database Records" />
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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">Reading Secondary Databases</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="secondaryProps.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="secondaryDelete.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="readSecondary"></a>Reading Secondary Databases</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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Like a primary database, you can read records from your secondary
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database either by using the
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<span>
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<code class="methodname">SecondaryDatabase.get()</code> method,
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</span>
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or by using
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<span>a <code class="classname">SecondaryCursor</code>.</span>
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The main difference between reading secondary and primary databases is that when
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you read a secondary database record, the secondary record's data is not
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returned to you. Instead, the primary key and data corresponding to the
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secondary key are returned to you.
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</p>
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<p>
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For example, assuming your secondary database contains keys related
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to a person's full name:
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</p>
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<a id="je_index6"></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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...
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try {
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// Omitting all database and environment opens
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...
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String searchName = "John Doe";
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DatabaseEntry searchKey =
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new DatabaseEntry(searchName.getBytes("UTF-8"));
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DatabaseEntry primaryKey = new DatabaseEntry();
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DatabaseEntry primaryData = new DatabaseEntry();
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// Get the primary key and data for the user 'John Doe'.
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OperationStatus retVal = mySecondaryDatabase.get(null, searchKey,
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primaryKey,
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primaryData,
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LockMode.DEFAULT);
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} catch (Exception e) {
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// Exception handling goes here
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}</pre>
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<p>
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Note that, just like
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<span><code class="methodname">Database.get()</code>, </span>
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if your secondary database supports duplicate records then
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<code class="methodname">SecondaryDatabase.get()</code>
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only return the first record found in a matching duplicates set. If you
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want to see all the records related to a specific secondary key, then use a
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<span>
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<code class="classname">SecondaryCursor</code> (described in <a class="xref" href="secondaryCursor.html" title="Using Secondary Cursors">
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<span>Using Secondary Cursors</span>
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</a>).
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</span>
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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="secondaryProps.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="secondaryDelete.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">Secondary Database Properties </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"> Deleting Secondary Database Records</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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