Delegate all calculations to the scope.

So that the scope may be a NullRelation and return a result without
executing a query.

Fixes #7928

2 files changed, 6 insertions, 4 deletions

diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index e044099b72..1b746b46b7 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -28,6 +28,8 @@ module ActiveRecord
     # is computed directly through SQL and does not trigger by itself the
     # instantiation of the actual post records.
     class CollectionProxy < Relation
+      delegate *ActiveRecord::Calculations.public_instance_methods, to: :scope
+
       def initialize(association) #:nodoc:
         @association = association
         super association.klass, association.klass.arel_table
@@ -965,10 +967,6 @@ module ActiveRecord
         proxy_association.reload
         self
       end
-
-      def pluck(column_names)
-        scope.pluck(column_names)
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/null_relation.rb b/activerecord/lib/active_record/null_relation.rb
index f8f7a6c976..711fc8b883 100644
--- a/activerecord/lib/active_record/null_relation.rb
+++ b/activerecord/lib/active_record/null_relation.rb
@@ -50,6 +50,10 @@ module ActiveRecord
       0
     end
 
+    def sum(*)
+      0
+    end
+
     def calculate(_operation, _column_name, _options = {})
       nil
     end