Re: [HACKERS] [PATCH] Generic type subscripting

From: Dmitry Dolgov <9erthalion6(at)gmail(dot)com>
To: Dian M Fay <dian(dot)m(dot)fay(at)gmail(dot)com>
Cc: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, 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: 2021-01-21 11:58:51
Message-ID: 20210121115851.3kwqkyks4irvf452@localhost
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> On Wed, Jan 20, 2021 at 11:37:32PM -0500, Dian M Fay wrote:
> On Wed Jan 20, 2021 at 2:08 PM EST, Dmitry Dolgov wrote:
> > > On Wed, Jan 20, 2021 at 11:34:16AM -0500, Dian M Fay wrote:
> > > > Thanks, I need to remember to not skipp doc building for testing process
> > > > even for such small changes. Hope now I didn't forget anything.
> > > >
> > > > > On Wed, Jan 20, 2021 at 09:58:43AM -0500, Dian M Fay wrote:
> > > >
> > > > > Here's a full editing pass on the documentation, with v45 and Pavel's
> > > > > doc-whitespaces-fix.patch applied. I also corrected a typo in one of the
> > > > > added hints.
> > > >
> > > > Great! I've applied almost all of it, except:
> > > >
> > > > + A <type>jsonb</type> value will accept assignments to nonexistent
> > > > subscript
> > > > + paths as long as the nonexistent elements being traversed are all
> > > > arrays.
> > > >
> > > > Maybe I've misunderstood the intention, but there is no requirement
> > > > about arrays for creating such an empty path. I've formulated it as:
> > > >
> > > > + A <type>jsonb</type> value will accept assignments to nonexistent
> > > > subscript
> > > > + paths as long as the last existing path key is an object or an array.
> > >
> > > My intention there was to highlight the difference between:
> > >
> > > * SET obj['a']['b']['c'] = '"newvalue"'
> > > * SET arr[0][0][3] = '"newvalue"'
> > >
> > > obj has to conform to {"a": {"b": {...}}} in order to receive the
> > > assignment of the nested c. If it doesn't, that's the error case we
> > > discussed earlier. But arr can be null, [], and so on, and any missing
> > > structure [[[null, null, null, "newvalue"]]] will be created.
> >
> > If arr is 'null', or any other scalar value, such subscripting will work
> > only one level deep because they represented internally as an array of
> > one element. If arr is '[]' the path will comply by definition. So it's
> > essentially the same as for objects with no particular difference. If
> > such a quirk about scalars being treated like arrays is bothering, we
> > could also bend it in this case as well (see the attached version).
>
> I missed that distinction in the original UPDATE paragraph too. Here's
> another revision based on v48.

Looks good, I've applied it, thanks.

Attachment Content-Type Size
v49-0001-Subscripting-for-jsonb.patch text/x-diff 45.6 KB
v49-0002-Filling-gaps-in-jsonb.patch text/x-diff 21.0 KB
v49-0003-Replace-assuming-a-composite-object-on-a-scalar.patch text/x-diff 9.6 KB

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