Edit File: secondaryCursor.html
<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title> Using Cursors with Secondary Databases </title> <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.62.4" /> <link rel="home" href="index.html" title="Getting Started with Berkeley DB" /> <link rel="up" href="indexes.html" title="Chapter 5. Secondary Databases" /> <link rel="previous" href="secondaryDelete.html" title="Deleting Secondary Database Records" /> <link rel="next" href="joins.html" title="Database Joins" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center"> Using Cursors with Secondary Databases </th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="secondaryDelete.html">Prev</a> </td> <th width="60%" align="center">Chapter 5. Secondary Databases</th> <td width="20%" align="right"> <a accesskey="n" href="joins.html">Next</a></td> </tr> </table> <hr /> </div> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="secondaryCursor"></a> <span>Using Cursors with Secondary Databases</span> </h2> </div> </div> <div></div> </div> <p> Just like cursors on a primary database, you can use <span>cursors on secondary databases</span> to iterate over the records in a secondary database. Like <span>cursors used with primary databases,</span> you can also use <span>cursors with secondary databases</span> to search for specific records in a database, to seek to the first or last record in the database, to get the next duplicate record, and so forth. For a complete description on cursors and their capabilities, see <a href="Cursors.html">Using Cursors</a>. </p> <p> However, when you use <span>cursors with secondary databases:</span> </p> <div class="itemizedlist"> <ul type="disc"> <li> <p> Any data returned is the data contained on the primary database record referenced by the secondary record. </p> </li> <li> <p> You cannot use <tt class="literal">DB_GET_BOTH</tt> and related flags with <tt class="methodname">DB->get()</tt> and a secondary database. Instead, you must use <span><tt class="methodname">DB->pget()</tt>.</span> Also, in that case the primary and secondary key given on the call to <tt class="methodname">DB->pget()</tt> must match the secondary key and associated primary record key in order for that primary record to be returned as a result of the call. </p> </li> </ul> </div> <p> For example, suppose you are using the databases, classes, and key <span>extractors</span> described in <a href="keyCreator.html">Implementing Key <span>Extractors</span> </a>. Then the following searches for a person's name in the secondary database, and deletes all secondary and primary records that use that name. </p> <a id="c_index8"></a> <pre class="programlisting">#include <db.h> #include <string.h> ... DB *sdbp; /* Secondary DB handle */ DBC *cursorp; /* Cursor */ DBT key, data; /* DBTs used for the delete */ char *search_name = "John Doe"; /* Name to delete */ /* Primary and secondary database opens omitted for brevity. */ /* Get a cursor on the secondary database */ sdbp->cursor(sdbp, NULL, &cursorp, 0); /* * Zero out the DBT before using it. */ memset(&key, 0, sizeof(DBT)); memset(&data, 0, sizeof(DBT)); key.data = search_name; key.size = strlen(search_name) + 1; /* Position the cursor */ while (cursorp->get(cursorp, &key, &data, DB_SET) == 0) cursorp->del(cursorp, 0); </pre> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="secondaryDelete.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="indexes.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="joins.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Deleting Secondary Database Records </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Database Joins</td> </tr> </table> </div> </body> </html>
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