Re: How to get column, table or parameter name reporting when violating DOMAIN type constraint

Thanks for the answer and explanation. My reasoning behind the use of
domains, particularly in function calls, is to have a useful approach for
validating input before it enters a function. By doing so, it eliminates
the need to manually verify input for public / exposed functions, and would
effectively make domains provide an efficient way to encapsulate and
enforce business rules.

Considering the aforementioned example, having a message reporting with the
position name would make the consumer life much easier, program or human
alike

SELECT my_function(100, -100);
-- ERROR: value "second_parameter" for domain my_domain violates check
constraint "value_min"

SELECT (-1)::my_domain;
-- ERROR: value "unnamed" for domain my_domain violates check
constraint "value_min"

Valerio

On Sun, 26 Mar 2023 at 18:00, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> "David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> > On Sunday, March 26, 2023, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> More to the point, you have the wrong mental model: a domain constraint
> >> violation might not be associated with a table column at all.
>
> > I disagree that the mental model is wrong.
>
> The OP is asking for action-at-a-distance. There are probably cases
> where the distance is short enough that we could associate the runtime
> error with a particular insertion target column, but I don't think it
> could possibly be made to work for every sort of insert/select query.
> In any case, the possibility of a hypothetical future feature (which
> nobody is actively working on AFAIK) doesn't seem like a very useful
> answer here.
>
> > There are existing threads that I may hunt later. IIRC, you (Tom) even
> > suggested a possible way forward on this last time it came up.
>
> I recall proposing that we try to produce syntax-error-like error
> cursors for runtime errors, but it's not apparent to me that that'd
> be tremendously applicable to the OP's problem. The output would
> look something like
>
> ERROR: value for domain my_domain violates check constraint "value_min"
> LINE 1: SELECT my_function(100, -100);
> ^
>
> which might be helpful for a human, but probably not very much so
> for a program. (BTW, this illustrates another issue: I'm pretty
> sure that in the given case, the error is thrown while evaluating
> my_function's arguments, long before we get within hailing distance
> of any INSERT at all.)
>
> regards, tom lane
>