Re: [HACKERS] [PATCH] Generic type subscripting

From: Dmitry Dolgov <9erthalion6(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, David Steele <david(at)pgmasters(dot)net>, Nikita Glukhov <n(dot)gluhov(at)postgrespro(dot)ru>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, David Fetter <david(at)fetter(dot)org>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Oleksandr Shulgin <oleksandr(dot)shulgin(at)zalando(dot)de>, Robert Haas <robertmhaas(at)gmail(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Oleg Bartunov <obartunov(at)gmail(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] [PATCH] Generic type subscripting
Date: 2020-12-17 20:00:33
Message-ID: 20201217200033.qdyjv4iimwyglnwt@localhost
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> On Thu, Dec 17, 2020 at 01:49:17PM -0500, Tom Lane wrote:
> 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.
>
> 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.

To be more specific, this is the current behaviour (an example from the
tests) and it doesn't seem right:

=# update test_jsonb_subscript
set test_json['a'] = 3 where id = 1;

UPDATE 1

=# select jsonb_typeof(test_json->'a')
from test_jsonb_subscript where id = 1;

jsonb_typeof
--------------
string

=# update test_jsonb_subscript
set test_json = jsonb_set(test_json, '{a}', '3') where id = 1;

UPDATE 1
=# select jsonb_typeof(test_json->'a')
from test_jsonb_subscript where id = 1;

jsonb_typeof
--------------
number

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