Re: constraint deferred but fails?

On 1/24/19 12:35 AM, Nagy László Zsolt wrote:

Hello,

I have deferred the only fk constraint to this table inside a
transaction, but I still cannot delete rows from it.

How is that possible?


master=> ALTER TABLE doc.display_mode disable trigger user;
ALTER TABLE
master=> BEGIN;
BEGIN
master=> SET CONSTRAINTS doc.fk_book_display_mode_id DEFERRED;
SET CONSTRAINTS
master=> DELETE FROM doc.display_mode;
ERROR:  update or delete on table "display_mode" violates foreign key
constraint "fk_book_display_mode_id" on table "book"
DETAIL:  Key (id)=(1) is still referenced from table "book".
master=>

Deferring a constraint doesn't mean "disappearing" the constraint; it just means... deferring it until later (i.e. commit time).  It's only purpose is to allow your code to delete from doc.display_mode before deleting from book .  But you do have to delete from book at some point in the transaction.