1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>Deleting Secondary Database Records</title> 7 <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.62.4" /> 9 <link rel="home" href="index.html" title="Getting Started with Berkeley DB" /> 10 <link rel="up" href="indexes.html" title="Chapter��5.��Secondary Databases" /> 11 <link rel="previous" href="readSecondary.html" title="Reading Secondary Databases" /> 12 <link rel="next" href="secondaryCursor.html" title=" Using Cursors with Secondary Databases " /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Deleting Secondary Database Records</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="readSecondary.html">Prev</a>��</td> 22 <th width="60%" align="center">Chapter��5.��Secondary Databases</th> 23 <td width="20%" align="right">��<a accesskey="n" href="secondaryCursor.html">Next</a></td> 24 </tr> 25 </table> 26 <hr /> 27 </div> 28 <div class="sect1" lang="en" xml:lang="en"> 29 <div class="titlepage"> 30 <div> 31 <div> 32 <h2 class="title" style="clear: both"><a id="secondaryDelete"></a>Deleting Secondary Database Records</h2> 33 </div> 34 </div> 35 <div></div> 36 </div> 37 <p> 38 In general, you 39 40 <span>will</span> 41 not modify a secondary database directly. In 42 order to modify a secondary database, you should modify the primary 43 database and simply allow DB to manage the secondary modifications for you. 44 </p> 45 <p> 46 However, as a convenience, you can delete 47 48 <span>secondary database</span> 49 records directly. Doing so causes the associated primary key/data pair to be deleted. 50 This in turn causes DB to delete all 51 52 <span>secondary database</span> 53 records that reference the primary record. 54 </p> 55 <p> 56 You can use the 57 58 59 <tt class="methodname">Db::del()</tt> 60 method to delete a secondary database record. 61 62 63 64 <span>Note that if your 65 <span>secondary database</span> 66 67 contains duplicate records, then deleting a record from the set of 68 duplicates causes all of the duplicates to be deleted as well. 69 </span> 70 71 </p> 72 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> 73 <h3 class="title">Note</h3> 74 <p> 75 76 <span> 77 You can delete a secondary database record using the previously 78 described mechanism 79 </span> 80 only if the primary database is opened for write access. 81 </p> 82 </div> 83 <p>For example:</p> 84 <a id="cxx_index7"></a> 85 <pre class="programlisting">#include <db_cxx.h> 86#include <string.h> 87 88... 89 90Db my_database(NULL, 0); // Primary 91Db my_index(NULL, 0); // Secondary 92 93// Open the primary 94my_database.open(NULL, // Transaction pointer 95 "my_db.db", // On-disk file that holds the database. 96 NULL, // Optional logical database name 97 DB_BTREE, // Database access method 98 DB_CREATE, // Open flags 99 0); // File mode (using defaults) 100 101// Setup the secondary to use sorted duplicates. 102// This is often desireable for secondary databases. 103my_index.set_flags(DB_DUPSORT); 104 105// Open the secondary 106my_index.open(NULL, // Transaction pointer 107 "my_secondary.db", // On-disk file that holds the database. 108 NULL, // Optional logical database name 109 DB_BTREE, // Database access method 110 DB_CREATE, // Open flags. 111 0); // File mode (using defaults) 112 113 114// Now associate the primary and the secondary 115my_database.associate(NULL, // Txn id 116 &my_index, // Associated secondary database 117 get_sales_rep, // Callback used for key extraction. 118 0); // Flags 119 120// Name to delete 121char *search_name = "John Doe"; 122 123// Get a search key 124Dbt key(search_name, strlen(search_name) + 1); 125 126// Now delete the secondary record. This causes the associated primary 127// record to be deleted. If any other secondary databases have secondary 128// records referring to the deleted primary record, then those secondary 129// records are also deleted. 130my_index.del(NULL, &key, 0); </pre> 131 </div> 132 <div class="navfooter"> 133 <hr /> 134 <table width="100%" summary="Navigation footer"> 135 <tr> 136 <td width="40%" align="left"><a accesskey="p" href="readSecondary.html">Prev</a>��</td> 137 <td width="20%" align="center"> 138 <a accesskey="u" href="indexes.html">Up</a> 139 </td> 140 <td width="40%" align="right">��<a accesskey="n" href="secondaryCursor.html">Next</a></td> 141 </tr> 142 <tr> 143 <td width="40%" align="left" valign="top">Reading Secondary Databases��</td> 144 <td width="20%" align="center"> 145 <a accesskey="h" href="index.html">Home</a> 146 </td> 147 <td width="40%" align="right" valign="top">�� 148 149 Using Cursors with Secondary Databases 150 </td> 151 </tr> 152 </table> 153 </div> 154 </body> 155</html> 156