On Thursday 26 January 2006 23:45, Joseph Kocherhans wrote: > Let's assume that MyModel.objects or my_object.related_set *IS* a > Query object (in other words, it has state):
It's state is simply an empty set of where clauses and an empty order by
list and these never actually change.
> q = MyModel.objects # q is Q1
> q.filter(*args) # q is still Q1, but with filters now
No, q.filter(*args) is a *new* set, it doesn't change q
> q.order_by('test') # q is still Q1 + filters + ordering
Again, a new set, which doesn't include the filter at all. The clone
would be done by the filter() and order_by() methods.
Unless I'm missing something about why that isn't possible?
> Ian Bicking has kept len() out of SQLObject result sets even though
> it seems really intuitive to use. Here's a rundown of what I remember
> about his argument: __len__ would run "count (*)" against the db. I
> think iter() calls len() implicitly for performance reasons, so you'd
> be running a useless count(*) every time you started iterating over a
> Query object. On the other hand, maybe if the iterator has already
> cahced the objects, __len__ could just call len() on the cache. It
> might be possible to work something out.
I'm happy with that, but I've done some quick tests and it doesn't seem
that __len__ is called when you get or use the iterator.
The only issue I've come across is that since managers are used to do
related object lookups, and related objects are cached, so are all
queries done by the manager - so iterating over Article.objects will
retrieve all the articles and keep them in a cache. But I imagine some
weakrefs will be adequate to sort that out.
Luke
--
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Luke Plant || L.Plant.98 (at) cantab.net || http://lukeplant.me.uk/
--
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Luke Plant || L.Plant.98 (at) cantab.net || http://lukeplant.me.uk/
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