1 files changed, 64 insertions, 0 deletions
diff --git a/lib/arel/algebra/relations/operations/join.rb b/lib/arel/algebra/relations/operations/join.rb
new file mode 100644
index 0000000000..e9320f28e1
--- /dev/null
+++ b/lib/arel/algebra/relations/operations/join.rb
@@ -0,0 +1,64 @@
+module Arel
+  class Join < Relation
+    attributes :relation1, :relation2, :predicates
+    deriving :==
+    delegate :name, :to => :relation1
+
+    def initialize(relation1, relation2 = Nil.instance, *predicates)
+      @relation1, @relation2, @predicates = relation1, relation2, predicates
+    end
+
+    def hash
+      @hash ||= :relation1.hash
+    end
+
+    def eql?(other)
+      self == other
+    end
+
+    def attributes
+      @attributes ||= (relation1.externalize.attributes +
+        relation2.externalize.attributes).collect { |a| a.bind(self) }
+    end
+
+    def wheres
+      # TESTME bind to self?
+      relation1.externalize.wheres
+    end
+
+    def ons
+      @ons ||= @predicates.collect { |p| p.bind(self) }
+    end
+
+    # TESTME
+    def externalizable?
+      relation1.externalizable? or relation2.externalizable?
+    end
+
+    def join?
+      true
+    end
+
+    def engine
+      relation1.engine != relation2.engine ? Memory::Engine.new : relation1.engine
+    end
+  end
+
+  class InnerJoin  < Join; end
+  class OuterJoin  < Join; end
+  class StringJoin < Join
+    def attributes
+      relation1.externalize.attributes
+    end
+
+    def engine
+      relation1.engine
+    end
+  end
+
+  class Relation
+    def join?
+      false
+    end
+  end
+end