Re: [HACKERS] [PATCH] Generic type subscripting

čt 17. 12. 2020 v 19:49 odesílatel Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> napsal:

> Dmitry Dolgov <9erthalion6(at)gmail(dot)com> writes:
> > While rebasing the jsonb patch I found out that the current subscripting
> > assignment implementation in transformAssignmentIndirection always
> > coerce the value to be assigned to the type which subscripting result
> > suppose to have (refrestype). For arrays it's fine, since those two
> > indeed must be the same, but for jsonb (and for hstore I guess too) the
> > result of subscripting is always jsonb (well, text type) and the
> > assigned value could be of some other type. This leads to assigning
> > everything converted to text.
>
> So ... what's the problem with that? Seems like what you should put
> in and what you should get out should be the same type.
>

I don't think so. For XML or JSON the target can be different, and it can
safe one CAST

DECLARE
n int;
v varchar;
js jsonb default '{"n": 100, "v" : "Hello"};
BEGIN
n := js['n'];
v := js['v'];

Can be nice to do this with a minimum number of transformations.

Regards

Pavel

> We can certainly reconsider the API for the parsing hook if there's
> really a good reason for these to be different types, but it seems
> like that would just be encouraging poor design.
>
> regards, tom lane
>