156 lines
5.9 KiB
HTML
156 lines
5.9 KiB
HTML
<?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>Deleting Secondary Database Records</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 V1.62.4" />
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<link rel="home" href="index.html" title="Getting Started with Berkeley DB" />
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<link rel="up" href="indexes.html" title="Chapter 5. Secondary Databases" />
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<link rel="previous" href="readSecondary.html" title="Reading Secondary Databases" />
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<link rel="next" href="secondaryCursor.html" title=" Using Cursors with Secondary Databases " />
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</head>
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<body>
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<div class="navheader">
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Deleting Secondary Database Records</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="readSecondary.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 5. Secondary Databases</th>
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<td width="20%" align="right"> <a accesskey="n" href="secondaryCursor.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="secondaryDelete"></a>Deleting Secondary Database Records</h2>
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</div>
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</div>
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<div></div>
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</div>
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<p>
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In general, you
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<span>will</span>
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not modify a secondary database directly. In
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order to modify a secondary database, you should modify the primary
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database and simply allow DB to manage the secondary modifications for you.
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</p>
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<p>
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However, as a convenience, you can delete
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<span>secondary database</span>
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records directly. Doing so causes the associated primary key/data pair to be deleted.
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This in turn causes DB to delete all
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<span>secondary database</span>
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records that reference the primary record.
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</p>
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<p>
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You can use the
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<tt class="methodname">Db::del()</tt>
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method to delete a secondary database record.
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<span>Note that if your
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<span>secondary database</span>
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contains duplicate records, then deleting a record from the set of
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duplicates causes all of the duplicates to be deleted as well.
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</span>
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</p>
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<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
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<h3 class="title">Note</h3>
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<p>
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<span>
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You can delete a secondary database record using the previously
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described mechanism
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</span>
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only if the primary database is opened for write access.
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</p>
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</div>
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<p>For example:</p>
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<a id="cxx_index7"></a>
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<pre class="programlisting">#include <db_cxx.h>
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#include <string.h>
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...
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Db my_database(NULL, 0); // Primary
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Db my_index(NULL, 0); // Secondary
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// Open the primary
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my_database.open(NULL, // Transaction pointer
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"my_db.db", // On-disk file that holds the database.
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NULL, // Optional logical database name
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DB_BTREE, // Database access method
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DB_CREATE, // Open flags
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0); // File mode (using defaults)
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// Setup the secondary to use sorted duplicates.
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// This is often desireable for secondary databases.
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my_index.set_flags(DB_DUPSORT);
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// Open the secondary
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my_index.open(NULL, // Transaction pointer
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"my_secondary.db", // On-disk file that holds the database.
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NULL, // Optional logical database name
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DB_BTREE, // Database access method
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DB_CREATE, // Open flags.
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0); // File mode (using defaults)
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// Now associate the primary and the secondary
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my_database.associate(NULL, // Txn id
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&my_index, // Associated secondary database
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get_sales_rep, // Callback used for key extraction.
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0); // Flags
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// Name to delete
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char *search_name = "John Doe";
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// Get a search key
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Dbt key(search_name, strlen(search_name) + 1);
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// Now delete the secondary record. This causes the associated primary
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// record to be deleted. If any other secondary databases have secondary
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// records referring to the deleted primary record, then those secondary
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// records are also deleted.
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my_index.del(NULL, &key, 0); </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="readSecondary.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="secondaryCursor.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">Reading Secondary Databases </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">
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Using Cursors with Secondary Databases
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</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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