Re: PATCH: Add hstore_to_json()

2010/1/4 David E. Wheeler <david(at)kineticode(dot)com>:
> On Jan 3, 2010, at 11:40 AM, Andrew Dunstan wrote:
>
>> We allow composites as fields. The biggest mismatch in the type model is probably w.r.t arrays. JSON arrays can be heterogenous and non-rectangular, AIUI.
>
> Cool, that sounds right.

Does it mean you should create composite type to create anonymous JSON?

>> OK, but hstores are flat, unlike JSON. We need some way to do the equivalent of xpath along the child axis and without predicate tests. hstore has no real equivalent because it has no nesting.
>
> You mean so that you can fetch a nested value? Hrm. I agree that it's have to be XPath like. But perhaps we can use a JavaScript-y syntax for it? There could be an operator that returns records:
>
>    % SELECT '{"foo":{"bar":["a","b","c"]}}' -> '["foo"]';
>         bar
>    -------------
>     ("{a,b,c}")
>
>    % SELECT '{"foo":{"bar":["a","b","c"]}}' -> '["foo"][1]';
>      1
>    -----
>     (b)
That sounds good and seems possible, as far as operator returns JSON
always. Perhaps every JSON fetching returns JSON even if the result
would be a number. You can cast it.

% SELECT ('{"foo":{"bar":["a","b","c"]}}' -> '["foo"][1]')::text;
1
-----
b

Regards,

--
Hitoshi Harada