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To: "Dmitry Dolgov" <9erthalion6@gmail.com>
Cc: "Pavel Stehule" <pavel.stehule@gmail.com>, "Tom Lane"
 <tgl@sss.pgh.pa.us>, "Andres Freund" <andres@anarazel.de>, "Alexander
 Korotkov" <aekorotkov@gmail.com>, "Justin Pryzby" <pryzby@telsasoft.com>,
 "David Steele" <david@pgmasters.net>, "Nikita Glukhov"
 <n.gluhov@postgrespro.ru>, "Alvaro Herrera" <alvherre@2ndquadrant.com>,
 "David Fetter" <david@fetter.org>, "Thomas Munro" <thomas.munro@gmail.com>,
 "Oleksandr Shulgin" <oleksandr.shulgin@zalando.de>, "Robert Haas"
 <robertmhaas@gmail.com>, "Michael Paquier" <michael.paquier@gmail.com>,
 "Oleg Bartunov" <obartunov@gmail.com>, "Peter Eisentraut"
 <peter.eisentraut@2ndquadrant.com>, "PostgreSQL Hackers"
 <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] [PATCH] Generic type subscripting
From: "Dian M Fay" <dian.m.fay@gmail.com>
Date: Wed, 20 Jan 2021 11:34:16 -0500
Message-Id: <C8O4PRM04CWJ.204R7D05JOJLB@lamia>
In-Reply-To: <20210120162231.4oht6mdp6v76xfhs@localhost>
Precedence: bulk

On Wed Jan 20, 2021 at 11:22 AM EST, Dmitry Dolgov wrote:
> > On Tue Jan 19, 2021 at 1:42 PM EST, Pavel Stehule wrote:
> >
> > I found minor issues.
> >
> > Doc - missing tag
> >
> > and three whitespaces issues
> >
> > see attached patch
>
> 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 th=
e
> > 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'] =3D '"newvalue"'
* SET arr[0][0][3] =3D '"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. Take 2:

A <type>jsonb</type> value will accept assignments to nonexistent
subscript paths as long as object key subscripts can be traversed as
described above. The final subscript is not traversed and, if it
describes a missing object key, will be created. Nested arrays will
always be created and <literal>NULL</literal>-padded according to the
path until the value can be placed appropriately.