Re: json, jsonb, and casts

Andrew Dunstan <andrew(dot)dunstan(at)pgexperts(dot)com> writes:
> In 9.3 we changed the way json generating functions worked by taking
> account of cast functions to json from non-builtin types, such as hstore.

> In 9.5 I am proposing to provide similar functionality for jsonb. The
> patch actually takes account of cast functions to both jsonb and json
> (with jsonb preferred). If there is a cast to jsonb, we use it and then
> merge the result into the jsonb being accumulated. If there is just a
> cast to json, we use it, and then parse that directly into the result
> datum.

> It was arguably a bit of an oversight not to take account of casts to
> jsonb in 9.4 in datum_to_json(). So I'm thinking of rolling into this
> patch changes to json.c::datum_to_json() and friends to take analogous
> account of casts to jsonb (i.e. call the cast function, turn the
> resulting jsonb into a cstring and append it to the result).

Meh. This leaves it very ambiguous which cast function would be applied
if both are available. I think it's overcomplicated anyway.

regards, tom lane