title: Multiple many-to-many relations to the same model in Django
body: <p>Given the following model with two many-to-many relations:</p>
  
  <pre><code>class Child(models.Model):
      name = models.CharField(max_length=80)
  
  class Foo(models.Model):
      bar = models.ManyToManyField(Child)
      baz = models.ManyToManyField(Child)
  </code></pre>
  
  <p>This gives the error:</p>
  
  <pre><code>accounts.foo: Accessor for m2m field 'bar' clashes with related m2m field 'Child.foo_set'. Add a related_name argument to the definition for 'bar'.
  accounts.foo: Accessor for m2m field 'baz' clashes with related m2m field 'Child.foo_set'. Add a related_name argument to the definition for 'baz'.
  </code></pre>
  
  <p>Fine; I don't need the backwards relation. <a href="https://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.ForeignKey.related_name" rel="noreferrer">According to the Django docs for related_name</a> (which is only under ForeignKey as far as I can see), I can set <code>related_name="+"</code> and backward relations won't be created:</p>
  
  <pre><code>class Child(models.Model):
      name = models.CharField(max_length=80)
  
  class Foo(models.Model):
      bar = models.ManyToManyField(Child, related_name="+")
      baz = models.ManyToManyField(Child, related_name="+")
  </code></pre>
  
  <p>This doesn't work though:</p>
  
  <pre><code>accounts.foo: Accessor for m2m field 'bar' clashes with related m2m field 'Child.+'. Add a related_name argument to the definition for 'bar'.
  accounts.foo: Reverse query name for m2m field 'bar' clashes with related m2m field 'Child.+'. Add a related_name argument to the definition for 'bar'.
  accounts.foo: Accessor for m2m field 'baz' clashes with related m2m field 'Child.+'. Add a related_name argument to the definition for 'baz'.
  accounts.foo: Reverse query name for m2m field 'baz' clashes with related m2m field 'Child.+'. Add a related_name argument to the definition for 'baz'.
  </code></pre>
  
  <p>What do I need to do to avoid creating reverse relations?</p>