3 files changed, 6 insertions, 9 deletions
diff --git a/activerecord/lib/active_record/dynamic_matchers.rb b/activerecord/lib/active_record/dynamic_matchers.rb
index f3f143940f..96a3a69d0d 100644
--- a/activerecord/lib/active_record/dynamic_matchers.rb
+++ b/activerecord/lib/active_record/dynamic_matchers.rb
@@ -63,9 +63,7 @@ module ActiveRecord
       def expand_attribute_names_for_aggregates
         attribute_names.map do |attribute_name|
           if aggregation = model.reflect_on_aggregation(attribute_name.to_sym)
-            model.send(:aggregate_mapping, aggregation).map do |field_attr, _|
-              field_attr.to_sym
-            end
+            aggregation.mapping.map { |m| m.first.to_sym }
           else
             attribute_name.to_sym
           end
@@ -240,10 +238,5 @@ module ActiveRecord
         "create!"
       end
     end
-
-    def aggregate_mapping(reflection)
-      mapping = reflection.options[:mapping] || [reflection.name, reflection.name]
-      mapping.first.is_a?(Array) ? mapping : [mapping]
-    end
   end
 end
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index d4f4d593c6..c380b5c029 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -153,6 +153,10 @@ module ActiveRecord
     # Holds all the meta-data about an aggregation as it was specified in the
     # Active Record class.
     class AggregateReflection < MacroReflection #:nodoc:
+      def mapping
+        mapping = options[:mapping] || [name, name]
+        mapping.first.is_a?(Array) ? mapping : [mapping]
+      end
     end
 
     # Holds all the meta-data about an association as it was specified in the
diff --git a/activerecord/lib/active_record/sanitization.rb b/activerecord/lib/active_record/sanitization.rb
index 81b13fe529..5530be3219 100644
--- a/activerecord/lib/active_record/sanitization.rb
+++ b/activerecord/lib/active_record/sanitization.rb
@@ -58,7 +58,7 @@ module ActiveRecord
         expanded_attrs = {}
         attrs.each do |attr, value|
           if aggregation = reflect_on_aggregation(attr.to_sym)
-            mapping = aggregate_mapping(aggregation)
+            mapping = aggregation.mapping
             mapping.each do |field_attr, aggregate_attr|
               if mapping.size == 1 && !value.respond_to?(aggregate_attr)
                 expanded_attrs[field_attr] = value