Subject: Postgres 17 domains with NOT NULL and pg_get_constraintdef()

From: [email-masked]
Date: Wed, 8 Jan 2025 12:15:19 +0100

Hello,

I am not sure if this is intended behavior or an oversight/bug.

Assume the following domain definition:

    CREATE DOMAIN sample_domain AS numeric(12,2) NOT NULL constraint positive_value CHECK (value > 0);

Up until Postgres 16 it was possible to retrieve the domain constraints using:

    select t.typname,
           pg_catalog.pg_get_constraintdef(ci.oid, true)
    from pg_catalog.pg_type t
      join pg_catalog.pg_constraint ci on ci.contypid = t.oid
    where t.typtype = 'd'
      and t.typname = 'sample_domain'

However, because the domain is defined with NOT NULL, this fails with

> ERROR: invalid constraint type "n"

with 17.2 on Windows and Linux.

This is a result of storing the NOT NULL constraint in pg_constraint
and can easily be avoided by either using contype <> 'n' or by not calling
pg_get_constraintdef if contype = 'n'

Is this a bug/oversight in pg_get_constraintdef() or does it just not support NOT NULL
constraints? The manual does not show any restriction on the usage.

---

From: Alvaro Herrera <[email-masked]>
Date: Wed, 8 Jan 2025 14:10:45 +0100

On 2025-Jan-08, [email-masked] wrote:

Hello,

> pg_get_constraintdef if contype = 'n'

Yeah, thanks for the report -- this is clearly a bug and it was fixed
already in the 17 branch, but it's not been released yet.  It'll be in
the February release.

Author: Álvaro Herrera <[email-masked]>
Branch: master [09d09d429] 2024-11-27 13:50:27 +0100
Branch: REL_17_STABLE [6e793582b] 2024-11-27 13:50:27 +0100

    Fix pg_get_constraintdef for NOT NULL constraints on domains
    
    We added pg_constraint rows for all not-null constraints, first for
    tables and later for domains; but while the ones for tables were
    reverted, the ones for domains were not.  However, we did accidentally
    revert ruleutils.c support for the ones on domains in 6f8bb7c1e961,
    which breaks running pg_get_constraintdef() on them.  Put that back.
    
    This is only needed in branch 17, because we've reinstated this code in
    branch master with commit 14e87ffa5c54.  Add some new tests in both
    branches.
    
    I couldn't find anything else that needs de-reverting.
    
    Reported-by: Erki Eessaar <[email-masked]>
    Reviewed-by: Magnus Hagander <[email-masked]>
    Discussion: https://postgr.es/m/[email-masked]

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Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
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