I have a class like this:
class Node:
name = models.CharField()
parents = models.ManyToManyField('self', symmetrical=False,
related_name='child_nodes', null=True, blank=True)
This allows a basic parent(s)/children hierarchy. A node can have >=
0 parents. A parent can have >= 0 children.
Say I have these nodes:
A - parent node
B - parent node
C - child of both A & B
So I can do this:
Node.objects.filter(name='C')
> returns ['C' node].
Node.objects.filter(name='C', parents__name='A')
> returns ['C' node].
Node.objects.filter(name='C', parents__name='B')
> returns ['C' node].
Node.objects.filter(Q(name='C'), Q(parents__name='A'))
> returns ['C' node].
Node.objects.filter(Q(name='C'), Q(parents__name='B'))
> returns ['C' node].
Node.objects.filter(Q(name='C'), Q(parents__name='A'),
Q(parents__name='B'))
> returns []
Node.objects.filter(Q(name='C') & Q(parents__name='A') &
Q(parents__name='B'))
> returns []
Node.objects.filter(Q(parents__name='A'), Q(parents__name='B'))
> returns []
Why do those last two return an empty set? I can even do this:
Node.objects.filter(Q(name='C'),
Q(parents__name='A')).filter(Q(parents__name='B'))
> returns ['C' node].
That works. But filtering on two parents (AND, not OR... I want the
child nodes of both parents) returns the empty set. It doesn't make
sense to me why using two separate filters would work, but combining
them into one statement gives different results.
Anyone have an idea about this? Is this a bug in the django query
system, or am I looking at this wrong? Thanks.
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