Horton

Re: [HACKERS] [PATCH] Generic type subscripting

Dmitry Dolgov <9erthalion6@gmail.com>

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From: Dmitry Dolgov <9erthalion6@gmail.com>
To: Pavel Stehule <pavel.stehule@gmail.com>
Cc: 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>
Date: 2020-12-22T16:16:23Z
Lists: pgsql-hackers

Attachments

> On Tue, Dec 22, 2020 at 12:19:26PM +0100, Pavel Stehule wrote:
>
> > Here is the new version of jsonb subscripting rebased on the committed
> > infrastructure patch. I hope it will not introduce any confusion with
> > the previously posted patched in this thread (about alter type subscript
> > and hstore) as they are independent.
> >
> > There are few differences from the previous version:
> >
> > * No limit on number of subscripts for jsonb (as there is no intrinsic
> >   limitation of this kind for jsonb).
> >
> > * In case of assignment via subscript now it expects the replace value
> >   to be of jsonb type.
> >
> > * Similar to the implementation for arrays, if the source jsonb is NULL,
> >   it will be replaced by an empty jsonb and the new value will be
> >   assigned to it. This means:
> >
> >         =# select * from test_jsonb_subscript where id = 3;
> >          id | test_json
> >         ----+-----------
> >           3 | NULL
> >
> >         =# update test_jsonb_subscript set test_json['a'] = '1' where id =
> > 3;
> >         UPDATE 1
> >
> >         =# select * from test_jsonb_subscript where id = 3;
> >          id | test_json
> >         ----+-----------
> >           3 | {"a": 1}
> >
> >   and similar:
> >
> >         =# select * from test_jsonb_subscript where id = 3;
> >          id | test_json
> >         ----+-----------
> >           3 | NULL
> >
> >         =# update test_jsonb_subscript set test_json[1] = '1' where id = 3;
> >         UPDATE 1
> >
> >         =# select * from test_jsonb_subscript where id = 3;
> >          id | test_json
> >         ----+-----------
> >           3 | {"1": 1}
> >
> >   The latter is probably a bit strange looking, but if there are any
> > concerns
> >   about this part (and in general about an assignment to jsonb which is
> > NULL)
> >   of the implementation it could be easily changed.
> >
>
> What is the possibility to make an array instead of a record?
>
> 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. To implement this we need to provide possibility for type
specific code to remember original subscript expression type (something
like in the attached version), which could be also useful for the future
work on jsonpath. I'm just not sure if there are again some important
bits are missing in this idea, so if someone can take a look I would
appreciate. In case there are any issues, I would just suggest keep it
simple and return NULL.

Commits

  1. Throw error when assigning jsonb scalar instead of a composite object

  2. Filling array gaps during jsonb subscripting

  3. Implementation of subscripting for jsonb

  4. Allow ALTER TYPE to update an existing type's typsubscript value.

  5. Allow subscripting of hstore values.

  6. Support subscripting of arbitrary types, not only arrays.

  7. jit: Reference function pointer types via llvmjit_types.c.

  8. Teach contain_leaked_vars that assignment SubscriptingRefs are leaky.

  9. jit: Correct parameter type for generated expression evaluation functions.

  10. Renaming for new subscripting mechanism

  11. Fix assertion failure for SSL connections.

  12. Teach eval_const_expressions() to handle some more cases.