Re: check foreign constraints before delete

On Wed, Sep 21, 2005 at 11:43:23PM +0000, Robert Wimmer wrote:
> i want to write a function in plpgsql, which checks a foreign key
> constraint violation on deleting a special value in my table. for example
>
> CREATE TABLE to (n NAME PRIMARY KEY);
> CREATE TABLE t1 (n_name NAME REFERENCES to(n), id INTEGER ...);
>
> CREATE FUNCTION check_before_delete(..some value ...) RETURNS INTEGER AS '
> ..
> IF foreign_key_violation THEN RETURN -1 END IF;
> RETURN 0;
> ..
> END;

In PostgreSQL 8.0 you could use an EXCEPTION clause:

http://www.postgresql.org/docs/8.0/interactive/plpgsql-control-structures.html#PLPGSQL-ERROR-TRAPPING

--
Michael Fuhr