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Prevent creation of too many associated rows in postgresql trigger.
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| CREATE TRIGGER "Q_limit_answers_per_question" AFTER INSERT or UPDATE on question_answer | |
| FOR EACH ROW EXECUTE PROCEDURE question_answer_insert(); | |
| CREATE OR REPLACE FUNCTION question_answer_insert() | |
| RETURNS TRIGGER AS | |
| $body$ | |
| BEGIN | |
| -- Lock the existing rows to prevent race condition with other txns. | |
| PERFORM * FROM question_answer WHERE question_id = NEW.question_id for UPDATE; | |
| -- Only allow insert/update if doesn't violate the constraints. | |
| IF (SELECT count(id) FROM question_answer where question_id = NEW.question_id) > 4 | |
| THEN | |
| RAISE EXCEPTION 'Too many rows for question %', NEW.question_id; | |
| END IF; | |
| RETURN NEW; | |
| END; | |
| $body$ | |
| LANGUAGE plpgsql; | |
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