Re: JSON in 9.2 - Could we have just one to_json() function instead of two separate versions ?

On 05/04/2012 09:52 AM, Tom Lane wrote:
> Hannu Krosing<hannu@2ndQuadrant.com>  writes:
>> On Wed, 2012-05-02 at 12:06 -0700, Andrew Dunstan wrote:
>>> So given that do we do anything about this now, or wait till 9.3?
>> I'd like the json support in 9.2 updated as follows
> I think it's too late to be entertaining proposals for such changes in
> 9.2.  If we had concluded that the existing functions were actively
> wrong or a bad idea, then of course we'd need to do something; but they
> are not, so we can just as well consider additions in the 9.3 cycle
> rather than now.  I am not convinced that this proposal is fully baked
> yet, anyway; not to mention that right now we need to have our heads
> down on resolving the remaining open issues, not designing,
> implementing, and reviewing a pile of brand new code for json.


Yeah, that was my feeling. We usually take a release or two to get 
things right, fill in what's missing, etc. and I don't think this will 
be ant different.


>
>> By allowing developers just to define their own to_json(date) function
>> we give them the power do decide which one to use. And if we honour
>> search_path when looking up the to_json() functions, then they can even
>> choose to have different conventions for different applications.
> This is not going to work anywhere near as nicely as you think.  If
> somebody tries to define multiple to_json() functions that override a
> generic to_json(anyelement) one, he will start getting "function is not
> unique" parse failures.  The parser will only successfully decide which
> function to call when the input data type exactly matches one of the
> specialized functions, which means you might as well not have the
> generic one at all.
>
>             

Yeah, what I've been thinking about in conjunction with similar problems 
is some sort of type registry, so that we could code for non-builtin 
types in certain cases. Maybe we should add that the the developers' 
meeting agenda.

cheers

andrew