QuerySet API .extra( ) usage for FIELD + ORDER BY of queryset

[Brandon]

I have reoccurring situation, when in a view.py function I need a queryset ordered by a set of identifiers. The order of those identifiers is dependent on factors outside of my control. Essentially in my view I am using modelformset_factory to generate a modelformset, then the usage of that modelformset instance requires queryset. It is that final queryset that must be ordered by the identifier whose order is externally determined.
So I use the .extra( ) function like below:

quali_results = ToxicologyCaseQualitativeResult.objects.filter(case_id=case.id).select_related('test').order_by('test__name')

field_list = ["AMPHS","BARB","BNZ","BE","Ecstasy","METH","6AM","PCP","THC"] #Usually populated via retrieval of user settings.
if len(field_list) > 0:
    field_list = field_list + [q.test.identifier for q in quali_results]
    fields = '"'+'","'.join(str(field) for field in field_list)+'"'
    field_sql = "FIELD(`identifier`,"+fields+")"
    quali_results = quali_results.extra(select={'field_sql' : field_sql}, order_by=['field_sql'])

quali_resultfs = QualitativeResultFormset(queryset=quali_results, prefix='quali_results')

If there is a better way to do this, I would be happy to change.
Cheers!
--Brandon

[Tim Graham]

I think that should be possible by writing your own ​Query Expression -- did you try it? If you have trouble, you can ask for help on our support channels. If that investigation shows that it's infeasible, please reopen the ticket with details.