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.

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