In general, you will 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.
However, as a convenience, you can delete secondary database records directly. Doing so causes the associated primary key/data pair to be deleted. This in turn causes DB to delete all secondary database records that reference the primary record.
You can use the Db::del() method to delete a secondary database record. Note that if your secondary database contains duplicate records, then deleting a record from the set of duplicates causes all of the duplicates to be deleted as well.
You can delete a secondary database record using the previously described mechanism only if the primary database is opened for write access.
For example:
#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);