3 files changed, 48 insertions, 16 deletions

diff --git a/lib/arel/algebra/primitives/attribute.rb b/lib/arel/algebra/primitives/attribute.rb
index 5e216770e4..943c5b030e 100644
--- a/lib/arel/algebra/primitives/attribute.rb
+++ b/lib/arel/algebra/primitives/attribute.rb
@@ -109,23 +109,23 @@ module Arel
 
     module Expressions
       def count(distinct = false)
-        distinct ?  Expression.new(self, "DISTINCT").count :  Expression.new(self, "COUNT")
+        distinct ?  Distinct.new(self).count :  Count.new(self)
       end
 
       def sum
-        Expression.new(self, "SUM")
+        Sum.new(self)
       end
 
       def maximum
-        Expression.new(self, "MAX")
+        Maximum.new(self)
       end
 
       def minimum
-        Expression.new(self, "MIN")
+        Minimum.new(self)
       end
 
       def average
-        Expression.new(self, "AVG")
+        Average.new(self)
       end
     end
     include Expressions
diff --git a/lib/arel/algebra/primitives/expression.rb b/lib/arel/algebra/primitives/expression.rb
index b67a5e1f8e..989397720c 100644
--- a/lib/arel/algebra/primitives/expression.rb
+++ b/lib/arel/algebra/primitives/expression.rb
@@ -1,12 +1,12 @@
 module Arel
   class Expression < Attribute
-    attributes :attribute, :function_sql, :alias, :ancestor
+    attributes :attribute, :alias, :ancestor
     deriving :==
     delegate :relation, :to => :attribute
     alias_method :name, :alias
 
-    def initialize(attribute, function_sql, aliaz = nil, ancestor = nil)
-      @attribute, @function_sql, @alias, @ancestor = attribute, function_sql, aliaz, ancestor
+    def initialize(attribute, aliaz = nil, ancestor = nil)
+      @attribute, @alias, @ancestor = attribute, aliaz, ancestor
     end
 
     def aggregation?
@@ -15,11 +15,11 @@ module Arel
 
     module Transformations
       def as(aliaz)
-        Expression.new(attribute, function_sql, aliaz, self)
+        self.class.new(attribute, aliaz, self)
       end
 
       def bind(new_relation)
-        new_relation == relation ? self : Expression.new(attribute.bind(new_relation), function_sql, @alias, self)
+        new_relation == relation ? self : self.class.new(attribute.bind(new_relation), @alias, self)
       end
 
       def to_attribute
@@ -28,4 +28,12 @@ module Arel
     end
     include Transformations
   end
+
+  class Count    < Expression; end
+  class Distinct < Expression; end
+  class Sum      < Expression; end
+  class Maximum  < Expression; end
+  class Minimum  < Expression; end
+  class Average  < Expression; end
 end
+
diff --git a/lib/arel/engines/sql/primitives.rb b/lib/arel/engines/sql/primitives.rb
index 5544d63710..c4968558a2 100644
--- a/lib/arel/engines/sql/primitives.rb
+++ b/lib/arel/engines/sql/primitives.rb
@@ -13,12 +13,6 @@ module Arel
     end
   end
 
-  class Expression < Attribute
-    def to_sql(formatter = Sql::SelectClause.new(relation))
-      formatter.expression self
-    end
-  end
-
   class Value
     def to_sql(formatter = Sql::WhereCondition.new(relation))
       formatter.value value
@@ -28,4 +22,34 @@ module Arel
       object.to_sql(Sql::Value.new(relation))
     end
   end
+  
+  class Expression < Attribute
+    def to_sql(formatter = Sql::SelectClause.new(relation))
+      formatter.expression self
+    end
+  end
+  
+  class Count < Expression
+    def function_sql; 'COUNT' end
+  end
+  
+  class Distinct < Expression
+    def function_sql; 'DISTINCT' end
+  end
+  
+  class Sum < Expression
+    def function_sql; 'SUM' end
+  end
+  
+  class Maximum < Expression
+    def function_sql; 'MAX' end
+  end
+  
+  class Minimum < Expression
+    def function_sql; 'MIN' end
+  end
+  
+  class Average < Expression
+    def function_sql; 'AVG' end
+  end
 end
\ No newline at end of file