| Current Path : /proc/2/cwd/usr/share/doc/db4-devel-4.7.25/gsg/CXX/ |
| Current File : //proc/2/cwd/usr/share/doc/db4-devel-4.7.25/gsg/CXX/secondaryDelete.html |
<?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>Deleting Secondary Database Records</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="readSecondary.html" title="Reading Secondary Databases" />
<link rel="next" href="secondaryCursor.html" title=" Using Cursors with Secondary Databases " />
</head>
<body>
<div class="navheader">
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">Deleting Secondary Database Records</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="readSecondary.html">Prev</a> </td>
<th width="60%" align="center">Chapter 5. Secondary Databases</th>
<td width="20%" align="right"> <a accesskey="n" href="secondaryCursor.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="secondaryDelete"></a>Deleting Secondary Database Records</h2>
</div>
</div>
<div></div>
</div>
<p>
In general, you
<span>will</span>
not modify a secondary database directly. In
order to modify a secondary database, you should modify the primary
database and simply allow DB to manage the secondary modifications for you.
</p>
<p>
However, as a convenience, you can delete
<span>secondary database</span>
records directly. Doing so causes the associated primary key/data pair to be deleted.
This in turn causes DB to delete all
<span>secondary database</span>
records that reference the primary record.
</p>
<p>
You can use the
<tt class="methodname">Db::del()</tt>
method to delete a secondary database record.
<span>Note that if your
<span>secondary database</span>
contains duplicate records, then deleting a record from the set of
duplicates causes all of the duplicates to be deleted as well.
</span>
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
<span>
You can delete a secondary database record using the previously
described mechanism
</span>
only if the primary database is opened for write access.
</p>
</div>
<p>For example:</p>
<a id="cxx_index7"></a>
<pre class="programlisting">#include <db_cxx.h>
#include <string.h>
...
Db my_database(NULL, 0); // Primary
Db my_index(NULL, 0); // Secondary
// Open the primary
my_database.open(NULL, // Transaction pointer
"my_db.db", // On-disk file that holds the database.
NULL, // Optional logical database name
DB_BTREE, // Database access method
DB_CREATE, // Open flags
0); // File mode (using defaults)
// Setup the secondary to use sorted duplicates.
// This is often desireable for secondary databases.
my_index.set_flags(DB_DUPSORT);
// Open the secondary
my_index.open(NULL, // Transaction pointer
"my_secondary.db", // On-disk file that holds the database.
NULL, // Optional logical database name
DB_BTREE, // Database access method
DB_CREATE, // Open flags.
0); // File mode (using defaults)
// Now associate the primary and the secondary
my_database.associate(NULL, // Txn id
&my_index, // Associated secondary database
get_sales_rep, // Callback used for key extraction.
0); // Flags
// Name to delete
char *search_name = "John Doe";
// Get a search key
Dbt key(search_name, strlen(search_name) + 1);
// Now delete the secondary record. This causes the associated primary
// record to be deleted. If any other secondary databases have secondary
// records referring to the deleted primary record, then those secondary
// records are also deleted.
my_index.del(NULL, &key, 0); </pre>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="readSecondary.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="secondaryCursor.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">Reading Secondary Databases </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top">
Using Cursors with Secondary Databases
</td>
</tr>
</table>
</div>
</body>
</html>
Copyright 2K16 - 2K18 Indonesian Hacker Rulez
;?>)