On 09/23/2016 10:27 PM, Jim Nasby wrote:
On 9/23/16 2:42 AM, Heikki Linnakangas wrote:
How do we handle single-dimensional arrays of composite types at the
moment? At a quick glance, it seems that the composite types are just
treated like strings, when they're in an array. That's probably OK, but
it means that there's nothing special about composite types in
multi-dimensional arrays. In any case, we should mention that in the docs.
That is how they're handled, but I'd really like to change that. I've
held off because I don't know how to handle the backwards
incompatibility that would introduce. (I've been wondering if we might
add a facility to allow specifying default TRANSFORMs that should be
used for specific data types in specific languages.)
The converse case (a composite with arrays) suffers the same problem
(array is just treated as a string).
I take that back, I don't know what I was talking about. Without this
patch, an array of composite types can be returned, using any of the
three representations for the composite type explained in the docs: a
string, a sequence, or a dictionary. So, all these work, and return the
same value:
create table foo (a int4, b int4);
CREATE FUNCTION comp_array_string() RETURNS foo[] AS $$
return ["(1, 2)"]
$$ LANGUAGE plpythonu;
CREATE FUNCTION comp_array_sequence() RETURNS foo[] AS $$
return [[1, 2]]
$$ LANGUAGE plpythonu;
CREATE FUNCTION comp_array_dict() RETURNS foo[] AS $$
return [{"a": 1, "b": 2}]
$$ LANGUAGE plpythonu;
Jim, I was confused, but you agreed with me. Were you also confused, or
am I missing something?
Now, back to multi-dimensional arrays. I can see that the Sequence
representation is problematic, with arrays, because if you have a python
list of lists, like [[1, 2]], it's not immediately clear if that's a
one-dimensional array of tuples, or two-dimensional array of integers.
Then again, we do have the type definitions available. So is it really
ambiguous?
The string and dict representations don't have that ambiguity at all, so
I don't see why we wouldn't support those, at least.
- Heikki
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