Re: data to json enhancements

On 09/26/2012 01:46 PM, Tom Lane wrote:
> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
>> Drawing together various discussions both here and elsewhere (e.g. the
>> PostgresOpen hallway track) I propose to work on the following:
>> 1. make datum_to_json() honor a type's cast to json if it exists. The
>> fallback is to use the type's string representation, as now.
>> 2. add a cast hstore -> json (any others needed for core / contrib types ?)
>> 3. add a to_json(anyelement) function
>> 4. add a new aggregate function json_agg(anyrecord) -> json to simplify
>> and make more effecient turning a resultset into json.
>> Comments welcome.
> ISTM the notion of to_json(anyelement) was already heavily discussed and
> had spec-compliance issues ... in fact, weren't you one of the people
> complaining? What exactly does #3 mean that is different from the
> previous thread?

I thought I got shouted down on that issue. The main reason we didn't
include it was that it was getting rather late for those changes, IIRC -
we only just got in any json stuff at all in under the wire.

And in fact you can have a json value now that's not an array or object:

andrew=# select json '1' as num, json '"foo"' as txt;
num | txt
-----+-------
1 | "foo"

>
> Also, on reflection I'm not sure about commandeering cast-to-json for
> this --- aren't we really casting to "json member" or something like
> that? The distinction between a container and its contents seems
> important here. With a container type as source, it might be important
> to do something different if we're coercing it to a complete JSON
> value versus something that will be just one member. I'm handwaving
> here because I don't feel like going back to re-read the RFC, but
> it seems like something that should be considered carefully before
> we lock down an assumption that there can never be a difference.

I think in view of the above this would be moot, no?

cheers

andrew