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Using Cursors with Secondary Databases
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Using Cursors with Secondary Databases
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<span>Using Cursors with Secondary Databases</span>
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<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>.
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However, when you use
<span>cursors with secondary databases:</span>
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Any data returned is the data contained on the primary database
record referenced by the secondary record.
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<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.
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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>
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