New DatasetSet model

closes #1712 (closed)

TODO:

• create process dataset issue
• create new API endpoints issue

arkindex/project/serializer_fields.py

@@ -286,7 +286,7 @@ class DatasetSetsCountField(serializers.DictField):
             return None
         elts_count = {k.name: 0 for k in instance.sets.all()}
         elts_count.update(
-            DatasetElement.objects.filter(set__dataset_id=instance.id)
+            DatasetElement.objects.filter(set_id__in=instance.sets.values_list("id"))
             .values("set__name")
             .annotate(count=Count("id"))
             .values_list("set__name", "count")