title: AttributeError: 'xxx' object has no attribute 'yyy_set'
body: <p>I'm trying to reverse a <a href="https://stackoverflow.com/questions/15306897/django-reverse-lookup-of-foreign-keys">foreign key relationship</a> from one model to the another.  In my case, that means seeing all Groups objects (many) for a given FieldFacet object (one).</p>
  
  <p>I've tried using <code>field_object.groups_set</code> <a href="https://stackoverflow.com/questions/13849075/attributeerror-object-has-no-attribute-set">method as described here</a>, but i get the error:</p>
  
  <p><code>AttributeError: 'FieldFacet' object has no attribute 'groups_set'</code></p>
  
  <p>I have checked that (as is the accepted solution) I am importing the objects, and that i can refer to them bu name, and query their objects.</p>
  
  <p>My models look like this:</p>
  
  <pre><code>class FieldBase(models.Model):
      field = models.ForeignKey('Field', on_delete=models.CASCADE)
      ...
      class Meta:
          abstract = True
  class FieldFacet(FieldBase):
      ...
  
  class Groups(models.Model):
      field = models.ForeignKey('FieldFacet', related_name='facet_field', on_delete=models.CASCADE)
      ...
  
  ff = FieldFacet.objects.get(pk=1)
  ff.__dict__
  # output
  # {'_state': &lt;django.db.models.base.ModelState object at 0x7fa22b9865c0&gt;, 'id': 1, 'recipe_id': 1, 'field_id': 1, 'data_type': 'text', 'json_path': '_id', 'order': 0, 'normalization': True, 'stripping': True, 'intelligent_size_limit': 0, 'max_values': 10, 'sorting': 'count', 'groups': 'no', 'default_group': ''}
  
  gg = Groups.objects.all()
  for g in gg:
      print(g.__dict__)
  # output
  # {'_state': &lt;django.db.models.base.ModelState object at 0x7fa22b986b38&gt;, 'id': 4, 'field_id': 1, 'name': 'p', 'minimum': None, 'maximum': None, 'values': '7'}
  # {'_state': &lt;django.db.models.base.ModelState object at 0x7fa22b986ba8&gt;, 'id': 3, 'field_id': 1, 'name': 'second', 'minimum': 1, 'maximum': 3, 'values': None}
  # {'_state': &lt;django.db.models.base.ModelState object at 0x7fa22b986c18&gt;, 'id': 2, 'field_id': 1, 'name': 'text', 'minimum': None, 'maximum': None, 'values': 'list of text'}
  # {'_state': &lt;django.db.models.base.ModelState object at 0x7fa22b986c88&gt;, 'id': 1, 'field_id': 1, 'name': 'first', 'minimum': 5, 'maximum': 10, 'values': None}
  
  # problem here:
  gro = ff.groups_set
  # Traceback (most recent call last):
  # File "&lt;console&gt;", line 1, in &lt;module&gt;
  # AttributeError: 'FieldFacet' object has no attribute 'groups_set'
  </code></pre>
  
  <p>Why am i seeing this error?</p>