Re: [SQLObject] Indexed access to a SelectResults

[Matt G. <ma...@po...>]

On Thu, 2003-07-17 at 01:05, Ian Bicking wrote:
> On Wed, 2003-07-16 at 17:42, Matt Goodall wrote:
> > > It would, though, create a bunch of SELECTs, like SELECT blah
> > > LIMIT 1 OFFSET 0, SELECT blah LIMIT 1 OFFSET 1, etc.
> > > 
> > > The problem is the way you're using it.
> > 
> > Unfortunately, it's not my code - it's another package that is walking
> > the list using an index. I can probably change that package but
> > couldn't/shouldn't SQLObject be a bit more graceful under these
> > circumstances?
> 
> I don't know.  If the code is going to treat select results as a list, a
> list seems like a reasonable thing to use (i.e.,
> list(Whatever.select())).  

Perhaps you're right.

The best solution is probably to change the code I'm using to iterate
over the results in the normal manner. This code in question could
actually take a slice first which would work really nicely with
SQLObject. Something for me to look into.

> 
> You could, generically, have a proxy class that batches the fetches, and
> caches the results temporarily (while it's waiting for your code to do
> another loop).  There's no reason it has to have specific support for
> SQLObject either.  Maybe such a thing already exists (probably does in
> *someone's* code... maybe on the ASPN recipe site).

Now that's not a bad idea, thanks.

> 
> > To be honest, it's really the multiple COUNT calls that bother me as it
> > seems unnecessary. The multiple SELECT calls to retrieve the objects are
> > to be expected but can possibly be avoided.
> 
> Yeah.  That is weird.  Ah... after some effort, I'm afraid I found why
> it happens.  list() tries to get the length of the things it's
> converting. 

Are you sure it's that simple? I was just playing with exactly this idea
too and wrote the following code to experiment:

        class Test:
            def __init__(self):
                self.counter = 0
            def __iter__(self):
                return self
            def next(self):
                self.counter = self.counter + 1
                if self.counter > 5:
                    raise StopIteration()
                return self.counter
                                                                                        t = Test()
        a = list(t)
        print a         # ok up to here
        print len(t)    # this fails

The fact that creating the list did not fail implies that it is not
trying to get the length of t. I dunno though, it's very late here so I
may be missing something obvious.

- Matt

-- 
Matt Goodall, Pollenation Internet Ltd
w: http://www.pollenation.net
e: ma...@po...