Question

I have a table which we can call decks. Decks has an id used as its primary key along with some other attributes. The cards table contains a foreign key reference to the deck id and has a primary key of cardid as well. Another table exists called answers where its foreign key is the cardid.

So in order to delete from decks, the database requires I delete from answers first, then cards, and then finally from decks.

I would like to create a trigger which takes care of the first and second delete so that I only have to specify a delete statement from the decks table to completely destroy a deck.

Below is an example PostgreSQL trigger I’ve found, but I am not sure if its even possible to do what I am asking as I can find no examples online of anyone creating a trigger this way.

CREATE OR REPLACE FUNCTION autoCalculate() RETURNS TRIGGER AS $$
        BEGIN

        IF NEW.wins < 0 THEN
                RAISE EXCEPTION 'Wins cannot be negative';
        END IF;

        IF(OLD.wins <> NEW.wins_ OR (OLD.losses <> NEW.losses) THEN
                NEW.Winning_Percentage := calc_winning_percentage(NEW.Wins, NEW.Losses);
        END IF

        RETURN NEW;
        END;
$$ LANGUAGE plpgsql;

DROP TRIGGER update_winning_percentage ON standings;
CREATE TRIGGER update_winning_percentage BEFORE INSERT OR UPDATE ON standings
FOR EACH ROW EXECUTE PROCEDURE autoCalculate();

If anyone has knowledge to do this, if they could nudge me in the right direction or provide an example of how to do this I’d be grateful!

Answer 1

On your foreign key definitions use ON DELETE CASCADE and it will take care of this for you