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>Using Cursors with Secondary Databases</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="secondaryDelete.html" title="Deleting Secondary Database Records" /> 12 <link rel="next" href="joins.html" title="Database Joins" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center"> 19 20 <span>Using Cursors with Secondary Databases</span> 21 </th> 22 </tr> 23 <tr> 24 <td width="20%" align="left"><a accesskey="p" href="secondaryDelete.html">Prev</a>��</td> 25 <th width="60%" align="center">Chapter��5.��Secondary Databases</th> 26 <td width="20%" align="right">��<a accesskey="n" href="joins.html">Next</a></td> 27 </tr> 28 </table> 29 <hr /> 30 </div> 31 <div class="sect1" lang="en" xml:lang="en"> 32 <div class="titlepage"> 33 <div> 34 <div> 35 <h2 class="title" style="clear: both"><a id="secondaryCursor"></a> 36 37 <span>Using Cursors with Secondary Databases</span> 38 </h2> 39 </div> 40 </div> 41 </div> 42 <p> 43 Just like cursors on a primary database, you can use 44 45 <span>cursors on secondary databases</span> 46 to iterate over the records in a secondary database. Like 47 48 49 <span>cursors used with primary databases,</span> 50 51 you can also use 52 53 <span>cursors with secondary databases</span> 54 to search for specific records in a database, to seek to the first 55 or last record in the database, to get the next duplicate record, 56 57 and so forth. For a complete description on cursors and their capabilities, see 58 <a class="xref" href="Cursors.html" title="Chapter��4.��Using Cursors">Using Cursors</a>. 59 </p> 60 <p> 61 However, when you use 62 63 <span>cursors with secondary databases:</span> 64 </p> 65 <div class="itemizedlist"> 66 <ul type="disc"> 67 <li> 68 <p> 69 Any data returned is the data contained on the primary database 70 record referenced by the secondary record. 71 </p> 72 </li> 73 <li> 74 <p> 75 You cannot use <code class="literal">DB_GET_BOTH</code> and related flags with 76 <code class="methodname">DB->get()</code> 77 78 and a secondary database. Instead, you must use 79 <span><code class="methodname">DB->pget()</code>.</span> 80 81 Also, in that case the primary and secondary key given on the call to 82 <code class="methodname">DB->pget()</code> 83 84 must match the secondary key and associated primary record key in 85 order for that primary record to be returned as a result of the 86 call. 87 </p> 88 </li> 89 </ul> 90 </div> 91 <p> 92 For example, suppose you are using the databases, classes, and key 93 94 <span>extractors</span> 95 described in <a class="xref" href="keyCreator.html" title="Implementing Key Extractors">Implementing Key 96 97 <span>Extractors</span> 98 </a>. 99 Then the following searches for a person's 100 name in the secondary database, and deletes all secondary and primary 101 records that use that name. 102 </p> 103 <a id="c_index8"></a> 104 <pre class="programlisting">#include <db.h> 105#include <string.h> 106 107... 108 109DB *sdbp; /* Secondary DB handle */ 110DBC *cursorp; /* Cursor */ 111DBT key, data; /* DBTs used for the delete */ 112char *search_name = "John Doe"; /* Name to delete */ 113 114/* Primary and secondary database opens omitted for brevity. */ 115 116/* Get a cursor on the secondary database */ 117sdbp->cursor(sdbp, NULL, &cursorp, 0); 118 119/* 120 * Zero out the DBT before using it. 121 */ 122memset(&key, 0, sizeof(DBT)); 123memset(&data, 0, sizeof(DBT)); 124 125key.data = search_name; 126key.size = strlen(search_name) + 1; 127 128 129/* Position the cursor */ 130while (cursorp->get(cursorp, &key, &data, DB_SET) == 0) 131 cursorp->del(cursorp, 0); </pre> 132 </div> 133 <div class="navfooter"> 134 <hr /> 135 <table width="100%" summary="Navigation footer"> 136 <tr> 137 <td width="40%" align="left"><a accesskey="p" href="secondaryDelete.html">Prev</a>��</td> 138 <td width="20%" align="center"> 139 <a accesskey="u" href="indexes.html">Up</a> 140 </td> 141 <td width="40%" align="right">��<a accesskey="n" href="joins.html">Next</a></td> 142 </tr> 143 <tr> 144 <td width="40%" align="left" valign="top">Deleting Secondary Database Records��</td> 145 <td width="20%" align="center"> 146 <a accesskey="h" href="index.html">Home</a> 147 </td> 148 <td width="40%" align="right" valign="top">��Database Joins</td> 149 </tr> 150 </table> 151 </div> 152 </body> 153</html> 154