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 <tt class="methodname">DB->del()</tt> 59 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="c_index7"></a> 85 <pre class="programlisting">#include <db.h> 86#include <string.h> 87 88... 89 90DB *dbp, *sdbp; /* Primary and secondary DB handles */ 91DBT key; /* DBTs used for the delete */ 92int ret; /* Function return value */ 93char *search_name = "John Doe"; /* Name to delete */ 94 95/* Primary */ 96ret = db_create(&dbp, NULL, 0); 97if (ret != 0) { 98 /* Error handling goes here */ 99} 100 101/* Secondary */ 102ret = db_create(&sdbp, NULL, 0); 103if (ret != 0) { 104 /* Error handling goes here */ 105} 106 107/* Usually we want to support duplicates for secondary databases */ 108ret = sdbp->set_flags(sdbp, DB_DUPSORT); 109if (ret != 0) { 110 /* Error handling goes here */ 111} 112 113/* open the primary database */ 114ret = dbp->open(dbp, /* DB structure pointer */ 115 NULL, /* Transaction pointer */ 116 "my_db.db", /* On-disk file that holds the database. 117 * Required. */ 118 NULL, /* Optional logical database name */ 119 DB_BTREE, /* Database access method */ 120 0, /* Open flags */ 121 0); /* File mode (using defaults) */ 122if (ret != 0) { 123 /* Error handling goes here */ 124} 125 126/* open the secondary database */ 127ret = sdbp->open(sdbp, /* DB structure pointer */ 128 NULL, /* Transaction pointer */ 129 "my_secdb.db", /* On-disk file that holds the database. 130 * Required. */ 131 NULL, /* Optional logical database name */ 132 DB_BTREE, /* Database access method */ 133 0, /* Open flags */ 134 0); /* File mode (using defaults) */ 135if (ret != 0) { 136 /* Error handling goes here */ 137} 138 139/* Now associate the secondary to the primary */ 140dbp->associate(dbp, /* Primary database */ 141 NULL, /* TXN id */ 142 sdbp, /* Secondary database */ 143 get_sales_rep, /* Callback used for key creation. */ 144 0); /* Flags */ 145 146/* 147 * Zero out the DBT before using it. 148 */ 149memset(&key, 0, sizeof(DBT)); 150 151key.data = search_name; 152key.size = strlen(search_name) + 1; 153 154/* Now delete the secondary record. This causes the associated primary 155 * record to be deleted. If any other secondary databases have secondary 156 * records referring to the deleted primary record, then those secondary 157 * records are also deleted. 158 */ 159 sdbp->del(sdbp, NULL, &key, 0); </pre> 160 </div> 161 <div class="navfooter"> 162 <hr /> 163 <table width="100%" summary="Navigation footer"> 164 <tr> 165 <td width="40%" align="left"><a accesskey="p" href="readSecondary.html">Prev</a> </td> 166 <td width="20%" align="center"> 167 <a accesskey="u" href="indexes.html">Up</a> 168 </td> 169 <td width="40%" align="right"> <a accesskey="n" href="secondaryCursor.html">Next</a></td> 170 </tr> 171 <tr> 172 <td width="40%" align="left" valign="top">Reading Secondary Databases </td> 173 <td width="20%" align="center"> 174 <a accesskey="h" href="index.html">Home</a> 175 </td> 176 <td width="40%" align="right" valign="top"> 177 178 Using Cursors with Secondary Databases 179 </td> 180 </tr> 181 </table> 182 </div> 183 </body> 184</html> 185