secondaryCursor.html [plain text]
<?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>
Using Cursors with 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 5. Secondary Databases" />
<link rel="previous" href="secondaryDelete.html" title="Deleting Secondary Database Records" />
<link rel="next" href="joins.html" title="Database Joins" />
</head>
<body>
<div class="navheader">
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">
Using Cursors with Secondary Databases
</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="secondaryDelete.html">Prev</a> </td>
<th width="60%" align="center">Chapter 5. Secondary Databases</th>
<td width="20%" align="right"> <a accesskey="n" href="joins.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="secondaryCursor"></a>
<span>Using Cursors with Secondary Databases</span>
</h2>
</div>
</div>
<div></div>
</div>
<p>
Just like cursors on a primary database, you can use
<span>cursors on secondary databases</span>
to iterate over the records in a secondary database. Like
<span>cursors used with primary databases,</span>
you can also use
<span>cursors with secondary databases</span>
to search for specific records in a database, to seek to the first
or last record in the database, to get the next duplicate record,
and so forth. For a complete description on cursors and their capabilities, see
<a href="Cursors.html">Using Cursors</a>.
</p>
<p>
However, when you use
<span>cursors with secondary databases:</span>
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
Any data returned is the data contained on the primary database
record referenced by the secondary record.
</p>
</li>
<li>
<p>
You cannot use <tt class="literal">DB_GET_BOTH</tt> and related flags with
<tt class="methodname">Db::get()</tt>
and a secondary database. Instead, you must use
<span><tt class="methodname">Db::pget()</tt>.</span>
Also, in that case the primary and secondary key given on the call to
<tt class="methodname">Db::pget()</tt>
must match the secondary key and associated primary record key in
order for that primary record to be returned as a result of the
call.
</p>
</li>
</ul>
</div>
<p>
For example, suppose you are using the databases, classes, and key
<span>extractors</span>
described in <a href="keyCreator.html">Implementing Key
<span>Extractors</span>
</a>.
Then the following searches for a person's
name in the secondary database, and deletes all secondary and primary
records that use that name.
</p>
<a id="cxx_index8"></a>
<pre class="programlisting">#include <db_cxx.h>
...
Db my_database(NULL, 0);
Db my_index(NULL, 0);
// Get a cursor on the secondary database
Dbc *cursorp;
my_index.cursor(NULL, &cursorp, 0);
// Name to delete
char *search_name = "John Doe";
// Instantiate Dbts as normal
Dbt key(search_name, strlen(search_name) + 1);
Dbt data;
// Position the cursor
while (cursorp->get(&key, &data, DB_SET) == 0)
cursorp->del(0); </pre>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="secondaryDelete.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="joins.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">Deleting Secondary Database Records </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> Database Joins</td>
</tr>
</table>
</div>
</body>
</html>