django orm optimization count on aggregates

app.py

results = myModel.objects.values().annotate(
  group_representative=ArrayAggFirstElem('pk', distinct=True),
)
group_representatives = results.values_list('group_representative', flat=True)

assert_(
    results.count() == group_representatives.count(),
    'Aggregation Spec should partition the results space (no overlaps)'
)