Horton

Re: [HACKERS] [PATCH] Generic type subscripting

Pavel Stehule <pavel.stehule@gmail.com>

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From: Pavel Stehule <pavel.stehule@gmail.com>
To: Dmitry Dolgov <9erthalion6@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: 2020-12-30T18:48:57Z
Lists: pgsql-hackers 
st 30. 12. 2020 v 14:46 odesílatel Dmitry Dolgov <9erthalion6@gmail.com>
napsal:

> > On Wed, Dec 30, 2020 at 02:45:12PM +0100, Dmitry Dolgov wrote:
> > > On Sat, Dec 26, 2020 at 01:24:04PM -0500, Tom Lane wrote:
> > >
> > > In a case like jsonpath['...'], the initially UNKNOWN-type literal
> could
> > > in theory be coerced to any of these types, so you'd have to resolve
> that
> > > case manually.  The overloaded-function code has an internal preference
> > > that makes it choose TEXT if it has a choice of TEXT or some other
> target
> > > type for an UNKNOWN input (cf parse_func.c starting about line 1150),
> but
> > > if you ask can_coerce_type() it's going to say TRUE for all three
> cases.
> > >
> > > Roughly speaking, then, I think what you want to do is
> > >
> > > 1. If input type is UNKNOWNOID, choose result type TEXT.
> > >
> > > 2. Otherwise, apply can_coerce_type() to see if the input type can be
> > > coerced to int4, text, or jsonpath.  If it succeeds for none or more
> > > than one of these, throw error.  Otherwise choose the single successful
> > > type.
> > >
> > > 3. Apply coerce_type() to coerce to the chosen result type.
> > >
> > > 4. At runtime, examine exprType() of the input to figure out what to
> do.
> >
> > Thanks, that was super useful. Following this suggestion I've made
> > necessary adjustments for the patch. There is no jsonpath support, but
> > this could be easily added on top.
>
> And the forgotten patch itself.
>

make check fails

But I dislike two issues

1. quietly ignored update

postgres=# update foo set a['a'][10] = '20';
UPDATE 1
postgres=# select * from foo;
┌────┐
│ a  │
╞════╡
│ {} │
└────┘
(1 row)

The value should be modified or there should be an error (but I prefer
implicit creating nested empty objects when it is necessary).

update foo set a['a'] = '[]';

2. The index position was ignored.

postgres=# update foo set a['a'][10] = '20';
UPDATE 1
postgres=# select * from foo;
┌─────────────┐
│      a      │
╞═════════════╡
│ {"a": [20]} │
└─────────────┘
(1 row)

Notes:

1. It is very nice so casts are supported. I wrote int2jsonb cast and it
was working. Maybe we can create buildin casts for int, bigint, numeric,
boolean, date, timestamp to jsonb.

Regards

Pavel

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.