On Thu, Jun 17, 2010 at 11:25 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Robert Haas <robertmh...@gmail.com> writes: >> On Thu, Jun 17, 2010 at 2:29 AM, Joseph Adams >> <joeyadams3.14...@gmail.com> wrote: >>> * No surprises when casting between JSON and TEXT. If approach B is >>> used, '"string"'::json would be '"string"', but '"string"'::json::text >>> would be 'string'. > >> As far as I'm concerned, that's a non-starter. It should be legal to >> cast text to json, but what it should do is validate that the string >> is already legal JSON, not quote it as a string. > > I'm not really convinced about that. It seems clear to me that there > are two behaviors that we'd like: > > 1. Take a string that is legal JSON, and make it into a JSON object. > > 2. Take an arbitrary string (or a number, a bool, etc) and make it a > literal value within a JSON object. > > We can make one of these behaviors be invoked by a cast, and the other > by an explicit function call --- the question is which is which.
Up to this point I agree. > I'm > inclined to think that associating #2 with casts might be better, > because clearly casting numerics or bools to JSON ought to act like #2. > If we do it as you suggest then casting text to JSON behaves differently > from casting anything else to JSON. I think this is going to turn into a thicket of semantic ambiguity. There are also two things you might want on output - (1) take a JSON object and export it as a string; (2) take a JSON object and extract from it some natively typed thing. So what happens, for example, when someone writes: json 'true' Do they get a JSON boolean or a JSON text? i.e. true or 'true'? Joseph's proposal also involved foo::text::json::text <> foo::text, which seems pretty ugly to me. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
