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Import BSDDB 4.7.25 (as of svn r89086)

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Zachary Ware
2017-09-04 13:40:25 -05:00
parent 4b29e0458f
commit 8f590873d0
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<?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>Reading Secondary Databases</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="indexes.html" title="Chapter 10. Secondary Databases" />
<link rel="previous" href="secondaryProps.html" title="Secondary Database Properties" />
<link rel="next" href="secondaryDelete.html" title="Deleting Secondary Database Records" />
</head>
<body>
<div class="navheader">
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">Reading Secondary Databases</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="secondaryProps.html">Prev</a> </td>
<th width="60%" align="center">Chapter 10. Secondary Databases</th>
<td width="20%" align="right"> <a accesskey="n" href="secondaryDelete.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="readSecondary"></a>Reading Secondary Databases</h2>
</div>
</div>
<div></div>
</div>
<p>
Like a primary database, you can read records from your secondary
database either by using the
<span>
<tt class="methodname">SecondaryDatabase.get()</tt> method,
</span>
or by using
<span>a <tt class="classname">SecondaryCursor</tt>.</span>
The main difference between reading secondary and primary databases is that when
you read a secondary database record, the secondary record's data is not
returned to you. Instead, the primary key and data corresponding to the
secondary key are returned to you.
</p>
<p>
For example, assuming your secondary database contains keys related
to a person's full name:
</p>
<a id="java_index6"></a>
<pre class="programlisting">package db.GettingStarted;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.OperationStatus;
import com.sleepycat.db.SecondaryDatabase;
...
SecondaryDatabase mySecondaryDatabase = null;
try {
// Omitting all database opens
...
String searchName = "John Doe";
DatabaseEntry searchKey =
new DatabaseEntry(searchName.getBytes("UTF-8"));
DatabaseEntry primaryKey = new DatabaseEntry();
DatabaseEntry primaryData = new DatabaseEntry();
// Get the primary key and data for the user 'John Doe'.
OperationStatus retVal = mySecondaryDatabase.get(null, searchKey,
primaryKey,
primaryData,
LockMode.DEFAULT);
} catch (Exception e) {
// Exception handling goes here
}</pre>
<p>
Note that, just like
<span><tt class="methodname">Database.get()</tt>, </span>
if your secondary database supports duplicate records then
<tt class="methodname">SecondaryDatabase.get()</tt>
only return the first record found in a matching duplicates set. If you
want to see all the records related to a specific secondary key, then use a
<span>
<tt class="classname">SecondaryCursor</tt> (described in <a href="secondaryCursor.html">
<span>Using Secondary Cursors</span>
</a>).
</span>
</p>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="secondaryProps.html">Prev</a> </td>
<td width="20%" align="center">
<a accesskey="u" href="indexes.html">Up</a>
</td>
<td width="40%" align="right"> <a accesskey="n" href="secondaryDelete.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">Secondary Database Properties </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> Deleting Secondary Database Records</td>
</tr>
</table>
</div>
</body>
</html>