[postgis-devel] Typmod Again

[Stephen Frost]

* Paul Ramsey (pramsey at cleverelephant.ca) wrote:
> 32 bits:
> Top 24 bits for SRID,
> Middle 6 bits for Type,
> Bottom 2 bits for Z/M flags.

Don't we only get 31 bits, since returning a negative value for typmod
is an indication of failure?

> The difficulty is not doing typmod, it's doing it without breaking
> backwards compatibility. I'm also currently running into some oddness
> with PgSQL not handing me the typmod in the _in function (which is
> required to enforce the restriction), even though one is defined on
> the column.

Could it be due to above, where you've mistakenly ended up returning a
negative value..?  Just a thought.

> There's some issues in general with typmod, I fear, which is that a
> typmod is not a constraint. Where is it enforced? It seems like only
> in the _in function, which just protects the on inserts from text.

That's a good point.  Have you looked at how it's done for NUMERIC?

> If I do
> 
> UPDATE mytable SET thegeom = ST_SetSRID(thegeom, 1111)
> 
> and 1111 is not my SRID typmod, what happens?

I would hope that there's an opportunity somewhere in the user defined
type code to handle this..  Does it go through the binary recv/send
functions?  If so, couldn't this check be handled there?

	Thanks,

		Stephen
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