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.
> 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)
And another that returns values where possible and JSON where there are data
structures.
% SELECT '{"foo":{"bar":["a","b","c"]}}' => '["foo"]';
?column?
------------------
{"bar":{a,b,c}"}
% SELECT '{"foo":{"bar":["a","b","c"]}}' => '["foo"][1]';
?column?
----------
b
Not sure if the same function can return different values, or if it's even
appropriate. In addition to returning JSON and TEXT as above, we'd also need to
be able to return numbers:
% SELECT '{"foo":{"bar":[22,42]}}' => '["foo"][1]';
?column?
----------
42
Thoughts?
David
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