diff --git a/core/inventory/shared_serializers.py b/core/inventory/shared_serializers.py
index 0bd44c3..2cafd5f 100644
--- a/core/inventory/shared_serializers.py
+++ b/core/inventory/shared_serializers.py
@@ -24,7 +24,7 @@ class BasicItemSerializer(serializers.ModelSerializer):
 
     def get_file(self, instance):
         if len(instance.files.all()) > 0:
-            return instance.files.all().order_by('-created_at')[0].hash
+            return sorted(instance.files.all(), key=lambda x: x.created_at, reverse=True)[0].hash
         return None
 
     def get_returned(self, instance):
diff --git a/core/tickets/api_v2.py b/core/tickets/api_v2.py
index 1ed7e02..1f2696d 100644
--- a/core/tickets/api_v2.py
+++ b/core/tickets/api_v2.py
@@ -21,7 +21,7 @@ from tickets.shared_serializers import RelationSerializer
 
 class IssueViewSet(viewsets.ModelViewSet):
     serializer_class = IssueSerializer
-    queryset = IssueThread.objects.all()
+    queryset = IssueThread.objects.all().prefetch_related('state_changes', 'comments', 'emails', 'emails__attachments', 'assignments', 'assignments__assigned_to__username', 'item_relation_changes', 'shipping_vouchers')
 
 
 class RelationViewSet(viewsets.ModelViewSet):
diff --git a/core/tickets/models.py b/core/tickets/models.py
index 2c14687..f7ddb7b 100644
--- a/core/tickets/models.py
+++ b/core/tickets/models.py
@@ -52,7 +52,11 @@ class IssueThread(SoftDeleteModel):
     @property
     def state(self):
         try:
-            return self.state_changes.order_by('-timestamp').first().state
+            state_changes = sorted(self.state_changes.all(), key=lambda x: x.timestamp, reverse=True)
+            if state_changes:
+                return state_changes[0].state
+            else:
+                return None
         except AttributeError:
             return 'none'
 
@@ -67,7 +71,11 @@ class IssueThread(SoftDeleteModel):
     @property
     def assigned_to(self):
         try:
-            return self.assignments.order_by('-timestamp').first().assigned_to
+            assignments = sorted(self.assignments.all(), key=lambda x: x.timestamp, reverse=True)
+            if assignments:
+                return assignments[0].assigned_to
+            else:
+                return None
         except AttributeError:
             return None
 
diff --git a/core/tickets/serializers.py b/core/tickets/serializers.py
index aae37ba..b7d8b28 100644
--- a/core/tickets/serializers.py
+++ b/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)