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📄 BerkeleyDB-Core-C-GSG.pdf(433.36 KB)
📄 CoreCursorUsage.html(12.37 KB)
📄 CoreDBAdmin.html(5.38 KB)
📄 CoreDbUsage.html(11.13 KB)
📄 CoreEnvUsage.html(6.19 KB)
📄 Cursors.html(5.98 KB)
📄 DBEntry.html(7.62 KB)
📄 DBOpenFlags.html(4.32 KB)
📄 DbUsage.html(17.74 KB)
📄 DeleteEntryWCursor.html(3.62 KB)
📄 Positioning.html(19.17 KB)
📄 PutEntryWCursor.html(8.17 KB)
📄 ReplacingEntryWCursor.html(4.87 KB)
📄 accessmethods.html(12.5 KB)
📄 btree.html(22.02 KB)
📄 cachesize.html(4.57 KB)
📄 concepts.html(8.63 KB)
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📄 coreindexusage.html(28.29 KB)
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📄 introduction.html(9.62 KB)
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📄 moreinfo.html(6.96 KB)
📄 preface.html(6.41 KB)
📄 readSecondary.html(5.19 KB)
📄 returns.html(4.45 KB)
📄 secondaryCursor.html(5.61 KB)
📄 secondaryDelete.html(6.53 KB)
📄 usingDbt.html(15.64 KB)

Editing: 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">
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    <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" />
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    <link rel="start" href="index.html" title="Getting Started with Berkeley DB" />
    <link rel="up" href="indexes.html" title="Chapter 5. Secondary Databases" />
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    <div xmlns="" class="navheader">
      <div class="libver">
        <p>Library Version 11.2.5.3</p>
      </div>
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        <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>
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      <hr />
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    <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>
      <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 
            
            <code class="methodname">DB-&gt;del()</code>
            
        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 &lt;db.h&gt;
#include &lt;string.h&gt;

...

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(&amp;dbp, NULL, 0);
if (ret != 0) {
  /* Error handling goes here */
}

/* Secondary */
ret = db_create(&amp;sdbp, NULL, 0);
if (ret != 0) {
  /* Error handling goes here */
}

/* Usually we want to support duplicates for secondary databases */
ret = sdbp-&gt;set_flags(sdbp, DB_DUPSORT);
if (ret != 0) {
  /* Error handling goes here */
}

/* open the primary database */
ret = dbp-&gt;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-&gt;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-&gt;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(&amp;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-&gt;del(sdbp, NULL, &amp;key, 0); </pre>
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          <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>
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          <td width="40%" align="right" valign="top"> 
        
        <span>Using Cursors with Secondary Databases</span>
    </td>
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