[DB-SIG] need some database API design advice

[Peter Eisentraut]

On ons, 2012-04-11 at 12:48 -0700, Chris Clark wrote:
> > rv = plpy.execute("some SQL command")
> > if rv.colnames() is not None:
> >      output(rv.colnames())
> > else:
> >      output("it's a utility command")
> 
> My 2 cents, I don't like any of them :-p
> 
> I prefer the last one modified slightly:
> 
>     rv = plpy.execute("some SQL command")
>     if rv.colnames():
>          output(rv.colnames())
>     else:
>          output("it's a utility command")
> 
> I.e. loose the None check.

That would misbehave if a result set exists but contains zero columns.
(Sounds strange, but it's possible.)  Which actually now makes me lean
toward throwing an exception.

> I'm not sure I like making an explicit 
> function call for the colnames. I.e. I think sticking with the pep249 
> description attribute is a better solution, the API already exist so 
> clone that (when possible) in your new api.

That would require populating this structure on every call, which would
be expensive for such a low-level API, or turning the attribute into a
fake function, which would be evil.  I think this is best left to the
plpydbapi layer on top of it.