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 V1.73.2" /> 9 <link rel="start" href="index.html" title="Getting Started with Berkeley DB" /> 10 <link rel="up" href="indexes.html" title="Chapter��5.��Secondary Databases" /> 11 <link rel="prev" 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> 36 <p> 37 In general, you 38 39 <span>will</span> 40 not modify a secondary database directly. In 41 order to modify a secondary database, you should modify the primary 42 database and simply allow DB to manage the secondary modifications for you. 43 </p> 44 <p> 45 However, as a convenience, you can delete 46 47 <span>secondary database</span> 48 records directly. Doing so causes the associated primary key/data pair to be deleted. 49 This in turn causes DB to delete all 50 51 <span>secondary database</span> 52 records that reference the primary record. 53 </p> 54 <p> 55 You can use the 56 57 <code class="methodname">DB->del()</code> 58 59 method to delete a secondary database record. 60 61 62 63 <span>Note that if your 64 <span>secondary database</span> 65 66 contains duplicate records, then deleting a record from the set of 67 duplicates causes all of the duplicates to be deleted as well. 68 </span> 69 70 </p> 71 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> 72 <h3 class="title">Note</h3> 73 <p> 74 75 <span> 76 You can delete a secondary database record using the previously 77 described mechanism 78 </span> 79 only if the primary database is opened for write access. 80 </p> 81 </div> 82 <p>For example:</p> 83 <a id="c_index7"></a> 84 <pre class="programlisting">#include <db.h> 85#include <string.h> 86 87... 88 89DB *dbp, *sdbp; /* Primary and secondary DB handles */ 90DBT key; /* DBTs used for the delete */ 91int ret; /* Function return value */ 92char *search_name = "John Doe"; /* Name to delete */ 93 94/* Primary */ 95ret = db_create(&dbp, NULL, 0); 96if (ret != 0) { 97 /* Error handling goes here */ 98} 99 100/* Secondary */ 101ret = db_create(&sdbp, NULL, 0); 102if (ret != 0) { 103 /* Error handling goes here */ 104} 105 106/* Usually we want to support duplicates for secondary databases */ 107ret = sdbp->set_flags(sdbp, DB_DUPSORT); 108if (ret != 0) { 109 /* Error handling goes here */ 110} 111 112/* open the primary database */ 113ret = dbp->open(dbp, /* DB structure pointer */ 114 NULL, /* Transaction pointer */ 115 "my_db.db", /* On-disk file that holds the database. 116 * Required. */ 117 NULL, /* Optional logical database name */ 118 DB_BTREE, /* Database access method */ 119 0, /* Open flags */ 120 0); /* File mode (using defaults) */ 121if (ret != 0) { 122 /* Error handling goes here */ 123} 124 125/* open the secondary database */ 126ret = sdbp->open(sdbp, /* DB structure pointer */ 127 NULL, /* Transaction pointer */ 128 "my_secdb.db", /* On-disk file that holds the database. 129 * Required. */ 130 NULL, /* Optional logical database name */ 131 DB_BTREE, /* Database access method */ 132 0, /* Open flags */ 133 0); /* File mode (using defaults) */ 134if (ret != 0) { 135 /* Error handling goes here */ 136} 137 138/* Now associate the secondary to the primary */ 139dbp->associate(dbp, /* Primary database */ 140 NULL, /* TXN id */ 141 sdbp, /* Secondary database */ 142 get_sales_rep, /* Callback used for key creation. */ 143 0); /* Flags */ 144 145/* 146 * Zero out the DBT before using it. 147 */ 148memset(&key, 0, sizeof(DBT)); 149 150key.data = search_name; 151key.size = strlen(search_name) + 1; 152 153/* Now delete the secondary record. This causes the associated primary 154 * record to be deleted. If any other secondary databases have secondary 155 * records referring to the deleted primary record, then those secondary 156 * records are also deleted. 157 */ 158 sdbp->del(sdbp, NULL, &key, 0); </pre> 159 </div> 160 <div class="navfooter"> 161 <hr /> 162 <table width="100%" summary="Navigation footer"> 163 <tr> 164 <td width="40%" align="left"><a accesskey="p" href="readSecondary.html">Prev</a>��</td> 165 <td width="20%" align="center"> 166 <a accesskey="u" href="indexes.html">Up</a> 167 </td> 168 <td width="40%" align="right">��<a accesskey="n" href="secondaryCursor.html">Next</a></td> 169 </tr> 170 <tr> 171 <td width="40%" align="left" valign="top">Reading Secondary Databases��</td> 172 <td width="20%" align="center"> 173 <a accesskey="h" href="index.html">Home</a> 174 </td> 175 <td width="40%" align="right" valign="top">�� 176 177 <span>Using Cursors with Secondary Databases</span> 178 </td> 179 </tr> 180 </table> 181 </div> 182 </body> 183</html> 184