4 files changed, 89 insertions, 0 deletions
diff --git a/lib/arel/relations/utilities/aggregation.rb b/lib/arel/relations/utilities/aggregation.rb
new file mode 100644
index 0000000000..66150bff0a
--- /dev/null
+++ b/lib/arel/relations/utilities/aggregation.rb
@@ -0,0 +1,40 @@
+module Arel
+  class Aggregation < Compound
+    include Recursion::BaseCase
+
+    def initialize(relation)
+      @relation = relation
+    end
+    
+    def wheres
+      []
+    end
+  
+    def table_sql(formatter = Sql::TableReference.new(relation))
+      formatter.select relation.select_sql, self
+    end
+  
+    def attributes
+      @attributes ||= relation.attributes.collect(&:to_attribute).collect { |a| a.bind(self) }
+    end
+    
+    def name
+      relation.name + '_aggregation'
+    end
+    
+    def ==(other)
+      Aggregation   === other and
+      self.relation ==  other.relation
+    end
+  end
+  
+  class Relation
+    def externalize
+      @externalized ||= aggregation?? Aggregation.new(self) : self
+    end
+    
+    def aggregation?
+      false
+    end
+  end
+end
+\ No newline at end of file
diff --git a/lib/arel/relations/utilities/compound.rb b/lib/arel/relations/utilities/compound.rb
new file mode 100644
index 0000000000..a77099e0de
--- /dev/null
+++ b/lib/arel/relations/utilities/compound.rb
@@ -0,0 +1,26 @@
+module Arel
+  class Compound < Relation
+    attr_reader :relation
+    hash_on :relation
+    delegate :joins, :wheres, :join?, :inserts, :taken,
+             :skipped, :name, :aggregation?, :column_for,
+             :engine, :table, :table_sql,
+             :to => :relation
+    
+    def attributes
+      @attributes ||= relation.attributes.collect { |a| a.bind(self) }
+    end
+    
+    def wheres
+      @wheres ||= relation.wheres.collect { |w| w.bind(self) }
+    end
+    
+    def groupings
+      @groupings ||= relation.groupings.collect { |g| g.bind(self) }
+    end
+    
+    def orders
+      @orders ||= relation.orders.collect { |o| o.bind(self) }
+    end
+  end
+end
+\ No newline at end of file
diff --git a/lib/arel/relations/utilities/nil.rb b/lib/arel/relations/utilities/nil.rb
new file mode 100644
index 0000000000..2dcfb47233
--- /dev/null
+++ b/lib/arel/relations/utilities/nil.rb
@@ -0,0 +1,10 @@
+module Arel
+  class Nil < Relation
+    def table_sql(formatter = nil); '' end
+    def name; '' end
+
+    def ==(other)
+      Nil === other
+    end
+  end
+end
+\ No newline at end of file
diff --git a/lib/arel/relations/utilities/recursion.rb b/lib/arel/relations/utilities/recursion.rb
new file mode 100644
index 0000000000..848b059507
--- /dev/null
+++ b/lib/arel/relations/utilities/recursion.rb
@@ -0,0 +1,13 @@
+module Arel
+  module Recursion
+    module BaseCase
+      def table
+        self
+      end
+
+      def table_sql(formatter = Sql::TableReference.new(self))
+        formatter.table self
+      end
+    end
+  end
+end
+\ No newline at end of file