  
      For use when performing full_clean on a model instance,
      so we only clean the required fields.
      """
      include = []
  
      if pk:
          # Deprecated
          pk_field = obj._meta.pk
          while pk_field.rel:
              pk_field = pk_field.rel.to._meta.pk
          include.append(pk_field.name)
  
 
</s> remove         include.append(pk_field.name)

    if slug_field:
        # Deprecated
        include.append(slug_field)

    if lookup_field and lookup_field != 'pk':
        include.append(lookup_field)
 </s> add         lookup_field = pk_field.name </s> remove def _get_validation_exclusions(obj, pk=None, slug_field=None, lookup_field=None):
 </s> add def _get_validation_exclusions(obj, lookup_field=None): </s> remove         lookup = self.kwargs.get(lookup_url_kwarg, None)
        pk = self.kwargs.get(self.pk_url_kwarg, None)
        slug = self.kwargs.get(self.slug_url_kwarg, None)
        slug_field = slug and self.slug_field or None

        if lookup:
            setattr(obj, self.lookup_field, lookup)

        if pk:
            setattr(obj, 'pk', pk)
 </s> add         lookup_value = self.kwargs[lookup_url_kwarg] </s> remove         if slug:
            setattr(obj, slug_field, slug)
 </s> add         setattr(obj, self.lookup_field, lookup_value) </s> remove             exclude = _get_validation_exclusions(obj, pk, slug_field, self.lookup_field)
 </s> add             exclude = _get_validation_exclusions(obj, self.lookup_field)
    if lookup_field == 'pk':
  
      For use when performing full_clean on a model instance,
      so we only clean the required fields.
      """
    if lookup_field == 'pk':
    if lookup_field == 'pk':
    if lookup_field == 'pk':
    if lookup_field == 'pk':
          pk_field = obj._meta.pk
          while pk_field.rel:
              pk_field = pk_field.rel.to._meta.pk
          include.append(pk_field.name)
  
keep keep keep keep replace replace replace replace keep keep keep keep keep
 Remove `pk_url_field`, `slug_url_field`, `slug_field`.

Closes #1773. 
rest_framework/mixins.py