Am 14.10.2010 um 23:07 schrieb Dan Watson:
> There seems to be some inconsistent behavior when combining querysets
> that use isnull on a ForeignKey. I'm not sure how to explain it well
> in plain english, so here's a boiled-down example:
>
> # Models
>
> class Item (models.Model):
> title = models.CharField( max_length=100 )
>
> class PropertyValue (models.Model):
> label = models.CharField( max_length=100 )
>
> class Property (models.Model):
> item = models.ForeignKey( Item, related_name='props' )
> key = models.CharField( max_length=100 )
> value = models.ForeignKey( PropertyValue, null=True )
>
> # Example
>
> item = Item.objects.create(title='Some Item')
> pv = PropertyValue.objects.create(label='Some Value')
> item.props.create(key='a', value=pv)
> item.props.create(key='b')
> q1 = Q(props__key='a', props__value=pv)
> q2 = Q(props__key='b', props__value__isnull=True)
> qs1 = Item.objects.filter(q1) & Item.objects.filter(q2)
> qs2 = Item.objects.filter(q2) & Item.objects.filter(q1)
>
> I would have expected qs1 and qs2 to yield the same result, but they
> do not. They should both return the single item, but qs1 returns
> nothing. The SQL for qs1 looks like:
>
> SELECT "app_item"."id", "app_item"."title" FROM "app_item"
> INNER JOIN "app_property" ON ("app_item"."id" =
> "app_property"."item_id")
> LEFT OUTER JOIN "app_property" T4 ON ("app_item"."id" = T4."item_id")
> LEFT OUTER JOIN "app_propertyvalue" T5 ON ("app_property"."value_id" =
> T5."id")
> WHERE (("app_property"."value_id" = 1 AND "app_property"."key" =
> 'a' ) AND (T5."id" IS NULL AND T4."key" = 'b' ))
>
> The first app_property join corresponds to q1, and the second
> corresponds to q2. However, the app_propertyvalue join (corresponding
> to the isnull from q2) refers to app_property.value_id (i.e. q1)
> instead of T4.value_id (i.e. q2). I think fixing #10790 would fix
> this, since removing the join to app_propertyvalue and simply checking
> "T4.value_id IS NULL" works as expected, but I'm not sure if this is a
> separate problem worthy of another ticket or not. Also (less
> importantly), since both criteria (q1 and q2) are checking
> props__key='something', I would imagine both joins could be INNER
> JOINs, but the isnull seems to promote the second to a LEFT OUTER
> JOIN.
>
> I guess I was just wondering if I should open a separate ticket for
> this, or is this simply a symptom of #10790? Or am I missing
> something?
Your problem looks like #11052 [1].
[1] http://code.djangoproject.com/ticket/11052
__
Johannes
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