Re: json function question

On 02/24/2016 09:41 AM, Tom Lane wrote:

> However, it looks to me like row_to_json already does pretty much the
> right thing with nested array/record types:
>
> regression=# select row_to_json(row(1,array[2,3],'(0,1)'::int8_tbl,array[(1,2),(3,4)]::int8_tbl[]));
> row_to_json
> ---------------------------------------------------------------------------------
> {"f1":1,"f2":[2,3],"f3":{"q1":0,"q2":1},"f4":[{"q1":1,"q2":2},{"q1":3,"q2":4}]}
> (1 row)
>
> So the complaint here is that json_populate_record fails to be an inverse
> of row_to_json.

Right.

>
> I'm not sure about Andrew's estimate that it'd be a large amount of work
> to fix this. It would definitely require some restructuring of the code
> to make populate_record_worker (or some portion thereof) recursive, and
> probably some entirely new code for array conversion; and making
> json_populate_recordset behave similarly might take refactoring too.
>
>

One possible shortcut if we were just handling arrays and not nested
composites would be to mangle the json array to produce a Postgres array
literal. But if we're handling nested composites as well that probably
won't pass muster and we would need to decompose all the objects fully
and reassemble them into Postgres objects. Maybe it won't take as long
as I suspect. If anyone actually does it I'll be interested to find out
how long it took them :-)

cheers

andrew