Speed up sql

core/tickets/serializers.py

@@ -63,14 +63,12 @@ class IssueSerializer(BasicIssueSerializer):
     @staticmethod
     def get_last_activity(self):
         try:
-            last_state_change = self.state_changes.order_by('-timestamp').first().timestamp \
-                if self.state_changes.count() > 0 else None
-            last_comment = self.comments.order_by('-timestamp').first().timestamp if self.comments.count() > 0 else None
-            last_mail = self.emails.order_by('-timestamp').first().timestamp if self.emails.count() > 0 else None
-            last_assignment = self.assignments.order_by('-timestamp').first().timestamp if \
-                self.assignments.count() > 0 else None
-            last_relation = self.item_relation_changes.order_by('-timestamp').first().timestamp if \
-                self.item_relation_changes.count() > 0 else None
+            last_state_change = max([t.timestamp for t in self.state_changes.all()]) if self.state_changes.exists() else None
+            last_comment = max([t.timestamp for t in self.comments.all()]) if self.comments.exists() else None
+            last_mail = max([t.timestamp for t in self.emails.all()]) if self.emails.exists() else None
+            last_assignment = max([t.timestamp for t in self.assignments.all()]) if self.assignments.exists() else None
+
+            last_relation = max([t.timestamp for t in self.item_relation_changes.all()]) if self.item_relation_changes.exists() else None
             args = [x for x in [last_state_change, last_comment, last_mail, last_assignment, last_relation] if
                     x is not None]
             return max(args)