Show subscribers counts in document change admin

costs/admin.py

@@ -21,8 +21,12 @@ class CostInline(admin.TabularInline):
 
 class ServiceInline(admin.TabularInline):
     model = Service
-    fields = ('name', 'monthly_unit_cost', 'new_subscriber_cost')
-    readonly_fields = ('name', 'monthly_unit_cost', 'new_subscriber_cost')
+    fields = (
+        'name', 'subscriptions_count',
+        'monthly_unit_cost', 'new_subscriber_cost')
+    readonly_fields = (
+        'name', 'subscriptions_count',
+        'monthly_unit_cost', 'new_subscriber_cost')
     show_change_link = True
     extra = 0