Horton

Re: [PATCH] Generic type subscripting

Peter Eisentraut <peter.eisentraut@2ndquadrant.com>

View thread View on postgr.es
From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
To: Dmitry Dolgov <9erthalion6@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2017-03-10T05:20:54Z
Lists: pgsql-hackers 
On 2/28/17 13:02, Dmitry Dolgov wrote:
> +<programlisting>
> +-- Extract value by key
> +SELECT ('{"a": 1}'::jsonb)['a'];
> +
> +-- Extract nested value by key path
> +SELECT ('{"a": {"b": {"c": 1}}}'::jsonb)['a']['b']['c'];
> +
> +-- Extract element by index
> +SELECT ('[1, "2", null]'::jsonb)['1'];
> +
> +-- Update value by key
> +UPDATE table_name set jsonb_field['key'] = 1;
> +
> +-- Select records using where clause with subscripting
> +SELECT * from table_name where jsonb_field['key'] = '"value"';
> +</programlisting>

I see a possible problem here:  This design only allows one subscripting
function.  But what you'd really want in this case is at least two: one
taking an integer type for selecting by array index, and one taking text
for selecting by field name.

I suppose that since a given value can only be either an array or an
object, there is no ambiguity, but I think this might also lose some
error checking.  It might also not work the same way for other types.

It looks like your jsonb subscripting function just returns null if it
can't find a field, which is also a bit dubious.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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.