joining across engines in either direction

Conflicts:

	spec/arel/engines/memory/integration/joins/cross_engine_spec.rb

1 files changed, 9 insertions, 1 deletions

diff --git a/lib/arel/algebra/relations/operations/join.rb b/lib/arel/algebra/relations/operations/join.rb
index 695f360b51..02a8fa629d 100644
--- a/lib/arel/algebra/relations/operations/join.rb
+++ b/lib/arel/algebra/relations/operations/join.rb
@@ -2,7 +2,7 @@ module Arel
   class Join < Relation
     attributes :relation1, :relation2, :predicates
     deriving :==
-    delegate :engine, :name, :to => :relation1
+    delegate :name, :to => :relation1
     hash_on :relation1
 
     def initialize(relation1, relation2 = Nil.instance, *predicates)
@@ -31,6 +31,10 @@ module Arel
     def join?
       true
     end
+    
+    def engine
+      relation1.engine != relation2.engine ? Memory::Engine.new : relation1.engine
+    end
   end
 
   class InnerJoin  < Join; end
@@ -39,6 +43,10 @@ module Arel
     def attributes
       relation1.externalize.attributes
     end
+    
+    def engine
+      relation1.engine
+    end
   end
 
   class Relation