Re: [SQLObject] Keeping the fields in order

[Carlos R. <car...@gm...>]

On Fri, 28 Jan 2005 18:53:30 -0600, Ian Bicking <ia...@co...> wrote:
> Carlos Ribeiro wrote:
> > Humm. A __getitem__/__setitem__ there would not do any harm IMHO. I
> > hope ou reconsider :-) But at the same time, an adapter may be enough
> > for this purpose.
> 
> A dictionary interface is just too ambiguous.  I can appreciate that it
> comes with a number of useful methods (like keys(), __contains__, etc)
> that feel missing compared to normal attributes.  But [] implies a level
> of dynamicism that I think isn't good.

I'm not sure I understand what do you mean with 'ambiguous'. One
possible concern is that access through the [] interface will happily
create new (key, item) pairs. In this case, a custom __setitem__ can
be designed so it traps it and raises an KeyError instead.

> > One potential application for this interface is to build automated
> > tools around SQLObject. For instance: report generators, form
> > generators, and the kind of scaffolding stuff that Rails is now famed
> > for. Of course, one can dive into SQLObject internals... but better
> > introspection methods would be helpful. A dict-like interface is
> > natural because __getitem__ style access is more convenient in this
> > scenario, to retrieve the necessary fields. BTW, I found myself using
> > getattr more often than I would care to admit.
> 
> I would agree there should be more clear, public methods for reflection
> in SQLObject, but I don't think there's anything wrong with getattr, and
> I don't think the dictionary interface is ultimately complete enough or
> extensible enough.

I think I expressed myself badly; there's nothing wrong with getattr
per se... but on the other hand, I believe that access via the
__getitem__ interface is still more convenient. But that may be a
matter of personal opinion. I think that, while we can overload
__getitem__ so it exposes only a few attributes of the object (in
SQLObject's case, just the columns), it's more difficult to do the
same with a getattr interface, which involves automatic lookup on the
class, superclasses, etc.

An example may help to clarify things: I would welcome the ability to
iterate over the columns of a SQLObject using iteritems() to build a
report, or a form, as in:

    for colname, value in Person.iteritems():
        print "%s: %s" % colname, value

The main advantage is familiarity: the iteritems() interface is well
know. It can return only the columns defined in the object, and that
seems to be intuitive enough for users to understand.

That said, I think that's a very interesting discussion. Let's the
issue rest a little bit; maybe we can gather more opinions... Best
regards, and have a nice weekend!

-- 
Carlos Ribeiro
Consultoria em Projetos
blog: http://rascunhosrotos.blogspot.com
blog: http://pythonnotes.blogspot.com
mail: car...@gm...
mail: car...@ya...