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<h2 class="title" style="clear: both"><a id="secondaryDelete"></a>Deleting Secondary Database Records</h2>
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<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>
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<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.
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<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>
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