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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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<p>
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="cxx_index8"></a>
<pre class="programlisting">#include <db_cxx.h>
...
Db my_database(NULL, 0);
Db my_index(NULL, 0);
// Get a cursor on the secondary database
Dbc *cursorp;
my_index.cursor(NULL, &cursorp, 0);
// Name to delete
char *search_name = "John Doe";
// Instantiate Dbts as normal
Dbt key(search_name, strlen(search_name) + 1);
Dbt data;
// Position the cursor
while (cursorp->get(&key, &data, DB_SET) == 0)
cursorp->del(0); </pre>
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