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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>
</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.
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<p>For example:</p>
<a id="cxx_index7"></a>
<pre class="programlisting">#include <db_cxx.h>
#include <string.h>
...
Db my_database(NULL, 0); // Primary
Db my_index(NULL, 0); // Secondary
// Open the primary
my_database.open(NULL, // Transaction pointer
"my_db.db", // On-disk file that holds the database.
NULL, // Optional logical database name
DB_BTREE, // Database access method
DB_CREATE, // Open flags
0); // File mode (using defaults)
// Setup the secondary to use sorted duplicates.
// This is often desireable for secondary databases.
my_index.set_flags(DB_DUPSORT);
// Open the secondary
my_index.open(NULL, // Transaction pointer
"my_secondary.db", // On-disk file that holds the database.
NULL, // Optional logical database name
DB_BTREE, // Database access method
DB_CREATE, // Open flags.
0); // File mode (using defaults)
// Now associate the primary and the secondary
my_database.associate(NULL, // Txn id
&my_index, // Associated secondary database
get_sales_rep, // Callback used for key extraction.
0); // Flags
// Name to delete
char *search_name = "John Doe";
// Get a search key
Dbt key(search_name, 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.
my_index.del(NULL, &key, 0); </pre>
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