Add support for ordering on expressions

Conflicts:

	lib/arel.rb
	lib/arel/attributes/attribute.rb
	lib/arel/nodes/infix_operation.rb
	lib/arel/nodes/named_function.rb

Conflicts:

	lib/arel.rb
	lib/arel/attributes/attribute.rb

lib/arel.rb

@@ -4,6 +4,7 @@ require 'arel/factory_methods'
 require 'arel/expressions'
 require 'arel/predications'
 require 'arel/math'
+require 'arel/order_predications'
 require 'arel/table'
 require 'arel/attributes'
 require 'arel/compatibility/wheres'

lib/arel/attributes/attribute.rb

@@ -3,6 +3,7 @@ module Arel
     class Attribute < Struct.new :relation, :name
       include Arel::Expressions
       include Arel::Predications
+      include Arel::OrderPredications
       include Arel::Math
 
       ###

lib/arel/expression.rb

@@ -1,4 +1,5 @@
 module Arel
   module Expression
+    include Arel::OrderPredications
   end
 end

lib/arel/nodes/sql_literal.rb

@@ -3,6 +3,7 @@ module Arel
     class SqlLiteral < String
       include Arel::Expressions
       include Arel::Predications
+      include Arel::OrderPredications
     end
   end
 end

lib/arel/order_predications.rb

@@ -0,0 +1,13 @@
+module Arel
+  module OrderPredications
+
+    def asc
+      Nodes::Ordering.new self, :asc
+    end
+
+    def desc
+      Nodes::Ordering.new self, :desc
+    end
+
+  end
+end

lib/arel/predications.rb

@@ -1,5 +1,6 @@
 module Arel
   module Predications
+
     def as other
       Nodes::As.new self, Nodes::SqlLiteral.new(other)
     end
@@ -152,14 +153,6 @@ module Arel
       grouping_all :lteq, others
     end
 
-    def asc
-      Nodes::Ordering.new self, :asc
-    end
-
-    def desc
-      Nodes::Ordering.new self, :desc
-    end
-
     private
 
     def grouping_any method_id, others

test/test_select_manager.rb

@@ -484,6 +484,29 @@ module Arel
         manager = Arel::SelectManager.new Table.engine
         manager.order(table[:id]).must_equal manager
       end
+
+      it 'has order attributes' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new Table.engine
+        manager.project SqlLiteral.new '*'
+        manager.from table
+        manager.order table[:id].desc
+        manager.to_sql.must_be_like %{
+          SELECT * FROM "users" ORDER BY "users"."id" DESC
+        }
+      end
+
+      it 'has order attributes for expressions' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new Table.engine
+        manager.project SqlLiteral.new '*'
+        manager.from table
+        manager.order table[:id].count.desc
+        manager.to_sql.must_be_like %{
+          SELECT * FROM "users" ORDER BY COUNT("users"."id") DESC
+        }
+      end
+
     end
 
     describe 'on' do