Re: [HACKERS] [PATCH] Generic type subscripting - Mailing list pgsql-hackers

> On Fri, Sep 18, 2020 at 07:23:11PM +0200, Pavel Stehule wrote:
>
> > In this way (returning an error on a negative indices bigger than the
> > number of elements) functionality for assigning via subscripting will be
> > already significantly differ from the original one via jsonb_set. Which
> > in turn could cause a new wave of something similar to "why assigning an
> > SQL NULL as a value returns NULL instead of jsonb?". Taking into account
> > that this is not absolutely new interface, but rather a convenient
> > shortcut for the existing one it probably makes sense to try to find a
> > balance between both consistency with regular array and similarity with
> > already existing jsonb modification functions.
> >
> > Having said that, my impression is that this balance should be not fully
> > shifted towards consistensy with the regular array type, as jsonb array
> > and regular array are fundamentally different in terms of
> > implementation. If any differences are of concern, they should be
> > addressed at different level. At the same time I've already sort of gave
> > up on this patch in the form I wanted to see it anyway, so anything goes
> > if it helps bring it to the finish point. In case if there would be no
> > more arguments from other involved sides, I can post the next version
> > with your suggestion included.
> >
>
> This is a relatively new interface and at this moment we can decide if it
> will be consistent or not.  I have not a problem if I have different
> functions with different behaviors, but I don't like one interface with
> slightly different behaviors for different types. I understand your
> argument about implementing a lighter interface to some existing API. But I
> think so more important should be consistency in maximall possible rate
> (where it has sense).
>
> For me "jsonb" can be a very fundamental type in PLpgSQL development - it
> can bring a lot of dynamic to this environment (it can work perfectly like
> PL/SQL collection or like Perl dictionary), but for this purpose the
> behaviour should be well consistent without surprising elements.

And here we are, the rebased version with the following changes:

    insert into test_jsonb_subscript values (1, '[]');
    update test_jsonb_subscript set test_json[5] = 1;
    select * from test_jsonb_subscript;
     id |             test_json
    ----+-----------------------------------
      1 | [null, null, null, null, null, 1]
    (1 row)

    update test_jsonb_subscript set test_json[-8] = 1;
    ERROR:  path element at position 1 is out of range: -8

Thanks for the suggestions!