#include <db.h> int DB->associate_foreign(DB *foreign, DB *secondary,, int (*callback)(DB *secondary, const DBT *key, DBT *data, const DBT *foreignkey, int *changed), u_int32_t flags);
The DB->associate_foreign() function is used to declare one database a
foreign constraint for a secondary database. The
DB handle that you call the
associate_foreign() method from is the foreign
database.
After a foreign database has been "associated" with a secondary
database, all keys inserted into the secondary must exist in the
foreign database. Attempting to add a record with a foreign key
that does not exist in the foreign database will cause the put
method to fail and return DB_FOREIGN_CONFLICT.
Deletions in the foreign database affect the secondary in a manner defined by the flags parameter. See Foreign Indices in the Berkeley DB Programmer's Reference Guide for more information.
The DB->associate_foreign()
method returns a non-zero error value on failure and 0 on success.
The callback parameter is a callback function that nullifies the foreign key portion of a data DBT.
The callback parameter must be NULL if either DB_FOREIGN_ABORT or DB_FOREIGN_CASCADE is set.
The callback takes four arguments:
secondary
The secondary parameter is the database handle for the secondary.
key
The key parameter is a DBT referencing the primary key.
data
The data parameter is a DBT referencing the primary data item to be updated.
foreignkey
The foreignkey parameter is a DBT referencing the foreign key which is being deleted.
changed
The changed parameter is a pointer to a boolean value, indicated whether data has changed.
Berkeley DB is not re-entrant. Callback functions should not attempt to make library calls (for example, to release locks or close open handles). Re-entering Berkeley DB is not guaranteed to work correctly, and the results are undefined.
The flags parameter must be set to one of the following values:
Abort the deletion of a key in the foreign database and return DB_FOREIGN_CONFLICT if that key exists in the secondary database. The deletion should be protected by a transaction to ensure database integrity after the aborted delete.
The deletion of a key in the foreign database will also delete that key from the secondary database (and the corresponding entry in the secondary's primary database.)
The deletion of a key in the foreign database will call the nullification function passed to associate_foreign and update the secondary database with the changed data.
The DB->associate_foreign()
method may fail and return one of the following non-zero errors:
When a client synchronizes with the master, it is possible for committed
transactions to be rolled back. This invalidates all the database and cursor
handles opened in the replication environment. Once this occurs, an attempt to use
such a handle will
return DB_REP_HANDLE_DEAD.
The application will need to discard the handle and open a new one in order to
continue processing.