Re: [HACKERS] [PATCH] Generic type subscripting

út 22. 12. 2020 v 18:35 odesílatel Dmitry Dolgov <9erthalion6(at)gmail(dot)com>
napsal:

> > On Tue, Dec 22, 2020 at 11:57:13AM -0500, Tom Lane wrote:
> > Dmitry Dolgov <9erthalion6(at)gmail(dot)com> writes:
> > > On Tue, Dec 22, 2020 at 12:19:26PM +0100, Pavel Stehule wrote:
> > >> I expect behave like
> > >>
> > >> update x set test[1] = 10; --> "[10]";
> > >> update x set test['1'] = 10; --> "{"1": 10}"
> >
> > > Yes, I also was thinking about this because such behaviour is more
> > > natural.
> >
> > I continue to feel that this is a fundamentally bad idea that will
> > lead to much more pain than benefit. People are going to want to
> > know why "test[1.0]" doesn't act like "test[1]". They are going
> > to complain because "test[$1]" acts so much differently depending
> > on whether they assigned a type to the $1 parameter or not. And
> > they are going to bitch because dumping and reloading a rule causes
> > it to do something different than it did before --- or at least we'd
> > be at horrid risk of that; only if we hide the injected cast-to-text
> > doesd the dumped rule look the way it needs to. Even then, the whole
> > thing is critically dependent on the fact that integer-type constants
> > are written and displayed differently from other constants, so it
> > won't scale to any other type that someone might want to treat specially.
> > So you're just leading datatype designers down a garden path that will be
> > a dead end for many of them.
> >
> > IMO this isn't actually any saner than your previous iterations
> > on the idea.
>
> Ok. While I don't have any preferences here, we can disregard the last
> posted patch (extended-with-subscript-type) and consider only
> v38-0001-Subscripting-for-jsonb version.
>

There are two parts - fetching and setting.

Probably there can be an agreement on fetching part: if index text is
JSONPath expression, use jsonb_path_query, else use jsonb_extract_path.
The setting should be the same in the inverse direction.

I like the behavior of jsonb_extract_path - it has intuitive behaviour and
we should use it.