Re: to_json(NULL) should to return JSON null instead NULL

2015-08-29 15:43 GMT+02:00 Shulgin, Oleksandr <oleksandr(dot)shulgin(at)zalando(dot)de>
:

> On Sat, Aug 29, 2015 at 3:39 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
>> > On 08/29/2015 08:47 AM, Shulgin, Oleksandr wrote:
>> >> Given there were no loud complaints about this, the current behavior
>> >> is appropriate for most users, the rest can still work around using
>> >> coalesce(to_json(...), json 'null').
>>
>> > I don't think it's necessarily more correct. But I do agree that it's
>> > not a good idea to change the behaviour unless there is major
>> > unhappiness with it.
>>
>> I'm not entirely convinced that JSON NULL and SQL NULL should be treated
>> as the same concept, so I would say that the current behavior is fine ---
>> at least when you think about it in isolation. However, haven't we
>> already bought into that equivalence in these examples?
>>
>> regression=# select row_to_json(row(1,null,2));
>> row_to_json
>> ---------------------------
>> {"f1":1,"f2":null,"f3":2}
>> (1 row)
>>
>> regression=# select array_to_json(array[1,null,2]);
>> array_to_json
>> ---------------
>> [1,null,2]
>> (1 row)
>>
>> or even in to_json itself:
>>
>> regression=# select to_json(array[1,null,2]);
>> to_json
>> ------------
>> [1,null,2]
>> (1 row)
>>
>> The scalar case is definitely failing to be consistent with these.
>>
>
> Yes, that's my argument for correctness also: to_json() on a composite
> object should behave like distribution of to_json() calls over object/array
> elements.
>
>
>> Is consistency a sufficient reason to change it?
>>
>
> Not for me.
>

It is bug - and it should be fixed. I agree, so this change is too strong
for fixing in minor version - but we can change it in unreleased major
versions - 9.5 and master.

Regards

Pavel

>
> --
> Alex
>
>