re-orgs into single query, assigns bar count to delete_count, rm incr…

…ement operation, re #10781

arches/app/models/graph.py

@@ -568,12 +568,12 @@ def delete_instances(self, verbose=False):
         deletes all associated resource instances
 
         """
+        resources_to_delete = list(Resource.objects.filter(graph_id=self.graphid))
+        delete_count = len(resources_to_delete)
         if verbose is True:
-            bar = pyprind.ProgBar(Resource.objects.filter(graph_id=self.graphid).count())
-        delete_count = 0
-        for resource in Resource.objects.filter(graph_id=self.graphid):
+            bar = pyprind.ProgBar(delete_count)
+        for resource in resources_to_delete:
             resource.delete()
-            delete_count += 1
             if verbose is True:
                 bar.update()
         if verbose is True: