Foreign keys in postgresql can be violated by trigger

Question

I've created some tables in postgres, added a foreign key from one table to another and set ON DELETE to CASCADE. Strangely enough, I have some fields that appear to be violating this constraint.

Is this normal behaviour? And if so, is there a way to get the behaviour I want (no violations possible)?

Edit:

I orginaly created the foreign key as part of CREATE TABLE, just using

... REFERENCES product (id) ON UPDATE CASCADE ON DELETE CASCADE

The current code pgAdmin3 gives is

ALTER TABLE cultivar
  ADD CONSTRAINT cultivar_id_fkey FOREIGN KEY (id)
      REFERENCES product (id) MATCH SIMPLE
      ON UPDATE CASCADE ON DELETE CASCADE;

Edit 2:

To Clarify, I have a sneaking suspicion that the constraints are only checked when updates/inserts happen but are then never looked at again. Unfortunately I don't know enough about postgres to find out if this is true or how fields could end up in the database without those checks being run.

If this is the case, is there some way to check all the foreign keys and fix those problems?

Edit 3:

A constraint violation can be caused by a faulty trigger, see below

Foreign keys in postgresql can be violated by trigger

2 Answers