On Wed, Jul 29, 2015 at 10:48 AM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> Corey Huinker <corey.huin...@gmail.com> writes: > > On Wed, Jul 29, 2015 at 3:48 AM, Heikki Linnakangas <hlinn...@iki.fi> > wrote: > >> Let's pursue the "CAST(srf() AS row_rtype)" syntax that Joe suggested > >> upthread ( > >> http://www.postgresql.org/message-id/559a9643.9070...@joeconway.com). > For > >> some reason, the discussion went on around the details of the submitted > >> patch after that, even though everyone seemed to prefer the CAST() > syntax. > > > I'm all for adding that syntax, but it wouldn't be useful for my purposes > > unless row_rtype could be a variable, and my understanding is that it > can't. > > Not sure why inserting a variable name is so much better than inserting a > type name? > > regards, tom lane > Apologies in advance if I'm going over things you already know. Just trying to package up the problem statement into something easily digestible. In a polymorphic function, I don't know the return type. It's whatever type was specified on the function call. Say I've written a function with a function like outer_polymorphic_function(p_rowtype anyelement,p1 ,p2,p3, ...) returns setof anyelement And inside that function is a series (probably a handful, but potentially thousands) of async dblink calls, and their corresponding calls to dblink_get_result(), which currently return setof record, each of which needs to be casted to whatever anyelement happens to be given this execution. Currently, I have to look up p_rowtype in pg_attribute and pg_class, render the column specs as valid SQL, and compose the query as a string fetch_values_query := 'select * from dblink_get_result($1) as t ( ' || 'c1 type, c2 othertype, ... ' || ')'; and then execute that dynamically like so: return query execute fetch_values_query using l_connection_name; It would be nice if I didn't have to resort to dynamic SQL do to this. If the CAST() function is implemented, but does not allow to cast as a variable, then I'm in the same boat: fetch_values_query := 'select * from CAST(dblink_get_result($1) as ' || pg_typeof(p_rowtype) || ')'; Admittedly, that's a bit cleaner, but I'm still executing that dynamic SQL once per connection I made, and there could be a lot of them. If there were dblink() functions that returned polymorphic results, it would be a non issue: dblink_send_query('conn1','select * from thing_i_know_is_shaped_like_my_rowtype') ... return query select * from dblink_get_result_any(p_rowtype,'conn1'); I'm all for the expanded capabilities of CAST(), but I have a specific need for polymorphic dblink() functions.
