Edit File: secondaryDelete.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>Deleting Secondary Database Records</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="readSecondary.html" title="Reading Secondary Databases" /> <link rel="next" href="secondaryCursor.html" title=" Using Cursors with Secondary Databases " /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">Deleting Secondary Database Records</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="readSecondary.html">Prev</a> </td> <th width="60%" align="center">Chapter 5. Secondary Databases</th> <td width="20%" align="right"> <a accesskey="n" href="secondaryCursor.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="secondaryDelete"></a>Deleting Secondary Database Records</h2> </div> </div> <div></div> </div> <p> In general, you <span>will</span> not modify a secondary database directly. In order to modify a secondary database, you should modify the primary database and simply allow DB to manage the secondary modifications for you. </p> <p> However, as a convenience, you can delete <span>secondary database</span> records directly. Doing so causes the associated primary key/data pair to be deleted. This in turn causes DB to delete all <span>secondary database</span> records that reference the primary record. </p> <p> You can use the <tt class="methodname">DB->del()</tt> method to delete a secondary database record. <span>Note that if your <span>secondary database</span> contains duplicate records, then deleting a record from the set of duplicates causes all of the duplicates to be deleted as well. </span> </p> <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> <h3 class="title">Note</h3> <p> <span> You can delete a secondary database record using the previously described mechanism </span> only if the primary database is opened for write access. </p> </div> <p>For example:</p> <a id="c_index7"></a> <pre class="programlisting">#include <db.h> #include <string.h> ... DB *dbp, *sdbp; /* Primary and secondary DB handles */ DBT key; /* DBTs used for the delete */ int ret; /* Function return value */ char *search_name = "John Doe"; /* Name to delete */ /* Primary */ ret = db_create(&dbp, NULL, 0); if (ret != 0) { /* Error handling goes here */ } /* Secondary */ ret = db_create(&sdbp, NULL, 0); if (ret != 0) { /* Error handling goes here */ } /* Usually we want to support duplicates for secondary databases */ ret = sdbp->set_flags(sdbp, DB_DUPSORT); if (ret != 0) { /* Error handling goes here */ } /* open the primary database */ ret = dbp->open(dbp, /* DB structure pointer */ NULL, /* Transaction pointer */ "my_db.db", /* On-disk file that holds the database. * Required. */ NULL, /* Optional logical database name */ DB_BTREE, /* Database access method */ 0, /* Open flags */ 0); /* File mode (using defaults) */ if (ret != 0) { /* Error handling goes here */ } /* open the secondary database */ ret = sdbp->open(sdbp, /* DB structure pointer */ NULL, /* Transaction pointer */ "my_secdb.db", /* On-disk file that holds the database. * Required. */ NULL, /* Optional logical database name */ DB_BTREE, /* Database access method */ 0, /* Open flags */ 0); /* File mode (using defaults) */ if (ret != 0) { /* Error handling goes here */ } /* Now associate the secondary to the primary */ dbp->associate(dbp, /* Primary database */ NULL, /* TXN id */ sdbp, /* Secondary database */ get_sales_rep, /* Callback used for key creation. */ 0); /* Flags */ /* * Zero out the DBT before using it. */ memset(&key, 0, sizeof(DBT)); key.data = search_name; key.size = strlen(search_name) + 1; /* Now delete the secondary record. This causes the associated primary * record to be deleted. If any other secondary databases have secondary * records referring to the deleted primary record, then those secondary * records are also deleted. */ sdbp->del(sdbp, NULL, &key, 0); </pre> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="readSecondary.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="secondaryCursor.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Reading Secondary Databases </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Using Cursors with Secondary Databases </td> </tr> </table> </div> </body> </html>
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