2 files changed, 18 insertions, 7 deletions
diff --git a/lib/active_relation/primitives/aggregation.rb b/lib/active_relation/primitives/aggregation.rb
index 48f8946835..26348fb35e 100644
--- a/lib/active_relation/primitives/aggregation.rb
+++ b/lib/active_relation/primitives/aggregation.rb
@@ -6,6 +6,10 @@ module ActiveRelation
       @attribute, @function_sql = attribute, function_sql
     end
 
+    def substitute(new_relation)
+      Aggregation.new(attribute.substitute(new_relation), function_sql)
+    end
+    
     def to_sql(strategy = nil)
       "#{function_sql}(#{attribute.to_sql})"
     end
diff --git a/lib/active_relation/primitives/attribute.rb b/lib/active_relation/primitives/attribute.rb
index 90bbe8012b..eb167b1a66 100644
--- a/lib/active_relation/primitives/attribute.rb
+++ b/lib/active_relation/primitives/attribute.rb
@@ -6,18 +6,25 @@ module ActiveRelation
       @relation, @name, @alias = relation, name, aliaz
     end
 
-    def as(aliaz = nil)
-      Attribute.new(relation, name, aliaz)
-    end
+    module Transformations
+      def as(aliaz = nil)
+        Attribute.new(relation, name, aliaz)
+      end
+    
+      def substitute(new_relation)
+        Attribute.new(new_relation, name, @alias)
+      end
 
+      def qualify
+        self.as(qualified_name)
+      end
+    end
+    include Transformations
+    
     def qualified_name
       "#{relation.name}.#{name}"
     end
 
-    def qualify
-      self.as(qualified_name)
-    end
-
     def ==(other)
       relation == other.relation and name == other.name and @alias == other.alias
     end