In article <roy-572c99.22201106032...@70-1-84-166.pools.spcsdns.net>,
Roy Smith <r...@panix.com> wrote:
> The problem is, QuerySets have a __len__() method. Calling it is a lot
> faster than iterating over the whole query set and counting the items,
> but it does result in an additional database query, which is a lot
> slower than the list resizing! Writing the code as a list comprehension
> prevents list() from trying to optimize when it shouldn't!
Hmmm, I think I've found a good solution.
It turns out, we don't actually use QuerySet in our models. We've
defined our own QuerySet subclass which adds a few convenience methods.
Adding
def __len__(self):
raise NotImplemented
to our subclass should do the job. It looks like list() respects that,
calls __iter__(), and does the right thing. I can't find any place
where that behavior for list() is documented, but it's logical and
experimentally, it seems to work.
Can anybody see any downside to this?
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