Re: Obtaining objects from a many-to-many relationship

On 12-06-02 1:15 AM, Kurtis Mullins wrote:

Have you tried b.haveone.all()?

Yes. Simplemindedly I wanted to try

B.haveone.all()

If I understand your suggestion, it would require iterating on instances of B to find all instances of A mentioned in B.

that would be something like

for b in B.objects.all():
  a = b.haveone.all()
  ...

which of course does work fine but may require visiting an instance of A more than once.

What I'm looking for is to select all unique instances of A which appear in B without iterating on B. Not all instances of A appearing in b (one specific instance of B).

tia

                 - Tom

On Sat, Jun 2, 2012 at 12:36 AM, Thomas Lockhart <tlockhart1976@gmail.com> wrote:

I've got two models with one having a many-to-many relationship with the other:

class A(models.Model):
 name = models.CharField("name")

class B(models.Model):
 haveone = models.ManyToManyField(A)

What is the idiom for getting all instances of A which are referenced in B? I found this works:

A.objects.annotate(n=models.Count('b')).filter(n__gt=0)

But istm that there is probably a more concise and straightforward way to accomplish this (and the solution is probably obvious but it is escaping me). tia

                 - Tom

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