Re: Fast-path FK checks reject valid inserts for domain-typed FK columns

Hi Ewan,

On Fri, Jun 12, 2026 at 12:36 PM Ewan Young <kdbase(dot)hack(at)gmail(dot)com> wrote:
>
> Hi,
>
> Commit 2da86c1 ("Add fast path for foreign key constraint checks") makes
> a foreign-key column whose type is a domain over a type different from
> the referenced PK reject every valid row:
>
> CREATE DOMAIN int8dom AS int8;
> CREATE TABLE pk (a int4 PRIMARY KEY);
> CREATE TABLE fk (b int8dom REFERENCES pk(a));
> INSERT INTO fk VALUES (1);
> ERROR: no conversion function from int8dom to integer
>
> It's new in v19 (verified by building 2da86c1^, where the insert
> succeeds); no released version is affected. The SPI path still handles
> it fine, e.g. with a partitioned PK.
>
> The fast path is the first caller to pass the cross-type pf_eq_oprs
> operator to ri_HashCompareOp(). Its "no cast needed" test,
>
> if (typeid == righttype)
>
> fails when the FK column is a domain over righttype (typeid is the
> domain OID), so it wrongly concludes no conversion exists and errors out.
> Looking through the domain fixes it -- conpfeqop is chosen against the
> FK base type, so getBaseType(typeid) == righttype holds for any valid FK:
>
> - if (typeid == righttype)
> + if (getBaseType(typeid) == righttype)
>
> Patch attached, with a regression test in foreign_key.sql. make check
> and the isolation suite pass.

Thanks for the report and the patch. Will look next week.

--
Thanks, Amit Langote