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: Alvaro Herrera <alvherre@2ndquadrant.com>, Thomas Munro <thomas.munro@enterprisedb.com>, Oleksandr Shulgin <oleksandr.shulgin@zalando.de>, Artur Zakirov <a.zakirov@postgrespro.ru>, Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, Andres Freund <andres@anarazel.de>, Michael Paquier <michael.paquier@gmail.com>, Oleg Bartunov <obartunov@gmail.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, David Steele <david@pgmasters.net>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2019-05-30T14:17:14Z
Lists: pgsql-hackers 
> On Wed, May 29, 2019 at 6:17 PM Pavel Stehule <pavel.stehule@gmail.com> wrote:
>
> st 29. 5. 2019 v 17:49 odesílatel Dmitry Dolgov <9erthalion6@gmail.com> napsal:
>>
>> Rebase after pg_indent. Besides, off the list there was a suggestion that this
>> could be useful to accept more than one data type as a key for subscripting.
>> E.g. for jsonb it probably makes sense to understand both a simple key name and
>> jsonpath:
>>
>>     jsonb['a'] and jsonb['$.a']
>>
>> While to implement it can be technically relatively straightforward I guess, I
>> wonder if there is any opinion about how valuable it could be and what it
>> should looks like from the syntax point of view (since I believe a user needs
>> to specify which type needs to be used).
>
>
> It is difficult decision - possibility to use jsonpath looks great, but
> necessity to cast every time is not friendly.

Thanks. Yes, I also wonder if it's possible to avoid type casting every time,
but other ideas seems syntactically equally not friendly.

> Probably there can be preferred type if subscripting is of unknown type.
> There can be similar rules to function's parameters.
>
> so jsonb['a'] -- key
>     jsonb['$.a'] -- key
>     jsonb['$.a'::jsonpath'] -- json path
>
> but it can be source of bad issues - so I think we don't need this feature in
> this moment. This feature can be implemented later, I think.

Yeah, I agree it's something that looks like a good potential improvement, not
now but in the future.

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.