Re: JSON manipulation functions

On Tue, May 25, 2010 at 10:52 AM, Joseph Adams
<joeyadams3(dot)14159(at)gmail(dot)com> wrote:
>> Well, I think it's fine to use the wiki for brainstorming, but before
>> you change the design you probably need to talk about it here.  You
>> can't rely on everyone on -hackers to follow changes on a wiki page
>> somewhere.  It looks like the API has been overhauled pretty heavily
>> since the last version we talked about here, and I'm not sure I
>> understand it.
>
> I'll try to explain it in one big nutshell:
>
> Instead of, for instance, json_to_number('5') and number_to_json(5), I
> propose changing it to from_json(5)::INT and to_json('5').  Note how
> from_json simply returns TEXT containing the underlying value for the
> user to cast.  I plan to make calling to_json/from_json with arrays or
> objects (e.g. to_json(ARRAY[1,2,3]) and from_json('[1,2,3]') ) throw
> an error for now, as implementing all the specifics of this could be
> quite distracting.

I don't see how that's an improvement over the previous design. It
seems like it adds a lot of extra casting and removes useful list
operations without any corresponding advantage.

> If I'm not mistaken, json_object([content [AS name] [, ...]] | *)
> RETURNS json can't be implemented without augmenting the grammar (as
> was done with xmlforest), so I considered making it take a RECORD
> parameter like the hstore(RECORD) function does, as was suggested on
> IRC.  However, this may be inadequate for selecting some columns but
> not others.  Using examples from hstore:
>
> SELECT hstore(foo) FROM foo;  => '"e"=>"2.71828", "pi"=>"3.14159"'
> -- this works, but what if we only want one field?
>
> SELECT hstore(pi) FROM foo;
> -- function type error
>
> SELECT hstore(row(pi)) FROM foo;  => '"f1"=>"3.14159"'
> -- field name is lost
>
> SELECT hstore(bar) FROM (select pi FROM foo) AS bar;  => '"f1"=>"3.14159"'
> -- ugly, and field name is *still* lost

Yeah. I'm not sure what to do about this problem.

--
Robert Haas
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