Switch Arel::Relation to a module. This will allow for classes with Relation extended on them to represent relations themselves (as opposed to their instances being relations).

5 files changed, 11 insertions, 7 deletions

diff --git a/lib/arel/algebra/relations/operations/join.rb b/lib/arel/algebra/relations/operations/join.rb
index df457686cc..300cd31bcd 100644
--- a/lib/arel/algebra/relations/operations/join.rb
+++ b/lib/arel/algebra/relations/operations/join.rb
@@ -1,5 +1,7 @@
 module Arel
-  class Join < Relation
+  class Join
+    include Relation
+
     attributes :relation1, :relation2, :predicates
     deriving :==
     delegate :name, :to => :relation1
@@ -60,7 +62,7 @@ module Arel
     end
   end
 
-  class Relation
+  module Relation
     def join?
       false
     end
diff --git a/lib/arel/algebra/relations/relation.rb b/lib/arel/algebra/relations/relation.rb
index 51c622cbe8..1c1ded15c9 100644
--- a/lib/arel/algebra/relations/relation.rb
+++ b/lib/arel/algebra/relations/relation.rb
@@ -1,5 +1,5 @@
 module Arel
-  class Relation
+  module Relation
     attr_reader :count
 
     def session
diff --git a/lib/arel/algebra/relations/utilities/compound.rb b/lib/arel/algebra/relations/utilities/compound.rb
index 0734842b27..7039b82575 100644
--- a/lib/arel/algebra/relations/utilities/compound.rb
+++ b/lib/arel/algebra/relations/utilities/compound.rb
@@ -1,5 +1,7 @@
 module Arel
-  class Compound < Relation
+  class Compound
+    include Relation
+
     attr_reader :relation
     delegate :joins, :join?, :inserts, :taken, :skipped, :name, :externalizable?,
              :column_for, :engine, :sources, :locked, :table_alias,
diff --git a/lib/arel/algebra/relations/utilities/externalization.rb b/lib/arel/algebra/relations/utilities/externalization.rb
index 13758ccec9..795a3919f2 100644
--- a/lib/arel/algebra/relations/utilities/externalization.rb
+++ b/lib/arel/algebra/relations/utilities/externalization.rb
@@ -12,7 +12,7 @@ module Arel
     end
   end
 
-  class Relation
+  module Relation
     def externalize
       @externalized ||= externalizable?? Externalization.new(self) : self
     end
diff --git a/lib/arel/algebra/relations/utilities/nil.rb b/lib/arel/algebra/relations/utilities/nil.rb
index 6a9d678c45..04055d0ddb 100644
--- a/lib/arel/algebra/relations/utilities/nil.rb
+++ b/lib/arel/algebra/relations/utilities/nil.rb
@@ -1,7 +1,7 @@
 require 'singleton'
 
 module Arel
-  class Nil < Relation
-    include Singleton
+  class Nil
+    include Relation, Singleton
   end
 end