Add graceful error-handling when a non-unique value is used for a SlugRelatedField

[allynt]

At the moment, if you specify a field that is not unique as the "slug_field" of a SlugRelatedField and the value you pass into the serializer matches multiple models then DRF will crash. This is in contrast to what happens when the value you pass matches zero models; then DRF handles the error gracefully.

I know that the documentation recommends only using unique fields as the "slug_field".

But it would be simple to add one more case to the following code:

django-rest-framework/rest_framework/relations.py

Lines 463 to 466 in 1ce0853

	except ObjectDoesNotExist:
	self.fail('does_not_exist', slug_name=self.slug_field, value=smart_str(data))
	except (TypeError, ValueError):
	self.fail('invalid')

Something like

except MultipleObjectsReturned:
    self.fail('multiple_objects', slug_name=self.slug_field, value=smart_str(data))

Obviously there would have to be a new "multiple_objects" entry added to the default_error_messages dictionary.

This would return a properly formatted 400 response when used correctly in a view instead of the current situation which raises a server error.

[auvipy]

that check would be nice to have. btw, can this be handled in django level?

[allynt]

@auvipy what do you mean by "django level"?