title: django many_to_many field deletion
body: <p>I have two django models which I want to connect using a many to many relationship. See the below example:</p>
  
  <pre><code>class A(models.Model):
      name = models.CharField(max_length=1000, unique=True)
  
  class B(models.Model):
      name = models.CharField(max_length=1000, unique=True)
      aa = models.ManyToManyField(A, related_name='bs', blank=True, null=True)
  </code></pre>
  
  <p>What I am trying to figure out is what happens if I delete a record of A or of B? What I want to have happen is that the relations in the M2M are deleted, but the other object stays intact. Say a row in A is deleted, then the related rows in B should remain, only the connection through the m2m relationship should be deleted. I can't find it in the Django documentation.</p>