On 09/26/2012 12:06 AM, Peter Eisentraut wrote:
On 9/25/12 5:58 PM, Tom Lane wrote:
Yes ... but I really don't want to go down the path of treating those as
new type properties; it doesn't scale. (And please don't tell me that
JSON is the last word in container types and there will never be
requests for any more of these.)
Yeah, I didn't like that part either, but we only add one every five
years or so.
Can we define these functions as being the cast-from-foo-to-json and
cast-from-foo-to-xml functions? That would let us use the existing cast
infrastructure to manage them.
Sounds attractive, but there might be some problems in the details. For
example, you can't cast scalar values to valid json values, because a
valid json value can only be a dictionary or an array.
Nope. Json _value_ can be anything you put in these dicts or arrays.
It was just definition about something called "a json generator" which
was defined to return an array or object/dict
and the json type already can hold all the scalar values, the input
conversion functions happily accept these and generate corresponding
json values.
It was all hashed through when I woke up on this too late in the 9.2 dev
cycle and proposed all the CAST and to_json functions and also a single
to_json for any json generation instead of array_to_json and row_to_json.
so currently we do and we don't have this "json is an array or dict"
functionality
we cant convert anything else directly to json using a to_json function,
but we can do it through input/output functions
and thus we can output scalar-valued json values :
jt=# select '1'::json,'"1"'::json;
json | json
------+------
1 | "1"
(1 row)
IIRC it was something about the to_json functions being generators and
type io
functions not being that :P
If we had a flag
of some kind saying "cast from foo to json, but only when part of a
larger json serialization, not by itself", then it might work.
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