[Django]-Django duplicate queries with manager related

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prefetch_related only works when you use .all().
If you apply any other transformations like .filter(), the new DB query will be made. This is because prefetch_related simply caches ALL related instances in list, so Django cannot perform filter() on list. To solve your issue you should use Prefetch object.
You can pass queryset parametr to it. So, instead of using list_prefetch_related, override get_queryset method in your admin class.

def get_queryset(*args, **kwargs):
     qs = super().get_queryset(*args, **kwargs)
     qs = qs.prefetch_related(Prefetch('c2app2_set', queryset=C2App2.objects.filter(is_ok=False)))
     return qs

And 

class C1App1(WithDateAndOwner):
   def get_c2_app2(self):
      res = self.c2app2_set.all()
      if res.count() > 0:
         return res[0]
      else:
         return None
👤Alexandr Tatarinov

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