On Mon, 2007-10-29 at 20:58 +0000, Kevin wrote:
> I'm trying to figure out how to chain filters for a many-to-many
> relation ship that is evaluating to an empty set when it should not. I
> basically have some a test with multiple dimms. I want to find a test
> with both dimm "sizes" 1024 & 2048.
>
> class TestLine(models.Model):
> #...some test info
>
> class Dimm(models.Model):
> testline = models.ForeignKey(TestLine)
> size = models.IntegerField()
>
> models.TestLine.objects.filter(dimm__size=1024).filter(dimm__size=2048)
>
> This returns an empty set, but I know there is a test with multiple
> dimm objects and meets this criteria. Is there a limitation that I'm
> missing here? Is there an alternative method to accomplish the intent
> here?
So I see you've found an alternative approach that works for now. The
underlying thing going on here is that there is a bug in the way Django
generates the SQL for many-to-many relations. If you try to filter on on
the same column more than once, it still only makes a single join to the
intermediary table, so you end up with things look like:
... where foo_id = 6 and foo_id = 7 ...
which is clearly impossible to satisfy for a unique column on the same
table.
This is ticket #1801 and has been fixed as part of the queryset-refactor
branch. When that work is complete, it'll be merged into trunk (the
branch is not suitable for testing yet)
Regards,
Malcolm
--
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