[postgis-devel] Typmod: Making my Life Harder

[Paul Ramsey]

Trying to think like a user, and taking into account some changes to
the typmod design. Note that I am doing this for GEOGRAPHY in the
first place, and GEOMETRY is not on the agenda until PostGIS 2.0.

So, first of all I have collapsed the dimensionality issues into the
type declarations. So you declare your type as:

POINT
POINTZ
POINTZM
LINESTRINGZ
...

And so on. That means that the typmod string signature is "only" two items long:

CREATE TABLE foo (g geography(4326, POINT));

However, for geography this gets further pointless as the initial
implementation is only going to accept 4326 as an SRID. And even when
it *does* accept alternates most people will just want to use 4326.
Also, one of the user targets for geography is geo-newbies, the folks
coming in with lonlat data and a dream. They shouldn't need to know
the "magic number", they should just need to be told "use geography,
go away".

CREATE TABLE foo (g geography(POINT));

So, should SRID be first? last? I'm actually thinking it could be
either, because I can test the arguments and if the argument is
numeric it is the srid and if it is letters that's the type. If we
want a fixed ordering, then I would now go for geography(type, srid).
I think for geometry, type *and* srid restrictions will be common, but
for geography, type-only restrictions will be the more frequent case.

P.