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 checkconstraint "value_min"
SELECT (-1)::my_domain; -- ERROR: value "unnamed" for domain my_domain violates checkconstraint "value_min"
"David G. Johnston" <david.g.johnston@gmail.com> writes: > On Sunday, March 26, 2023, Tom Lane <tgl@sss.pgh.pa.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.)
