It’s “almost safe”, in that the “trigger” will be called just before the deletion is performed. So if there isn’t something that goes on the little time lapse between “check” and the deletion operation, then everything is gonna be alright… (I guess)

A safer way would be to put the referential integrity (CONSTRAINT FOREIGN KEY ….) check also in the DBMS. (i.e. PostgreSQL and MySQL 5 supports this.) So even if something goes wrong in the application/Rails layer, the DBMS will catch it. It’s not so “DRY” (Don’t Repeat Yourself) but I think it’s a nice compromise… (and that is what I use)