Re: Domain Constraint Violation Error Messages

On 2018-07-25 17:23:21 +0200, Benjamin Coutu wrote:
> Please consider domains with domain constraints such as the following:
> 
>     CREATE DOMAIN "t_txt" text NOT NULL
>         CONSTRAINT "dc_txt" CHECK (VALUE <> '');
> 
>     CREATE DOMAIN "t_sha1" varchar(40) COLLATE "C" NOT NULL DEFAULT ''
>         CONSTRAINT "dc_sha1" CHECK (VALUE ~ '^([a-f0-9]{40})?$');
>         
> ... and some table such as this contrived example:
> 
>     CREATE TABLE "myusers" (
>         "name" "t_txt",
>         "email" "t_txt",
>         "token" "t_sha1"
>     );
>         
> Now, on inserting or updating the table with invalid data, appropriate domain constraint violations occur. But
unfortunatlythe associated error messages only reference the domain and not the underlying column, e.g. "ERROR: domain
public.t_txtdoes not allow null values".
 

If you have more verbose error messages turned on (the errors are always
transported to the client), you do get additional information:

terse:

postgres[15271][1]=# \set VERBOSITY terse
postgres[15271][1]=# INSERT INTO myusers (name, email, token) VALUES('', 'b', 'x');
ERROR:  value for domain t_txt violates check constraint "dc_txt"
Time: 0.803 ms

verbose:

postgres[15271][1]=# \set VERBOSITY verbose
postgres[15271][1]=# INSERT INTO myusers (name, email, token) VALUES('', 'b', 'x');
ERROR:  23514: value for domain t_txt violates check constraint "dc_txt"
SCHEMA NAME:  public
DATATYPE NAME:  t_txt
CONSTRAINT NAME:  dc_txt
LOCATION:  ExecEvalConstraintCheck, execExprInterp.c:3521
Time: 0.503 ms

That seems to address most of your complaint? Unfortunately the column
name is not available, as check constraints can involve more than one
column.

> I'm aware that this is not per se a bug, but without the column info,
> domains are somewhat useless for all practical purposes. Wouldn't you
> agree?

That still doesn't make this a bug. Please ask such questions on the
normal "user question" lists, not on bugs.

Greetings,

Andres Freund