better column disambiguation

4 files changed, 14 insertions, 8 deletions

diff --git a/lib/arel/primitives/attribute.rb b/lib/arel/primitives/attribute.rb
index 14b8c18cb2..5895f7e9b9 100644
--- a/lib/arel/primitives/attribute.rb
+++ b/lib/arel/primitives/attribute.rb
@@ -1,3 +1,5 @@
+require 'set'
+
 module Arel
   class Attribute
     attr_reader :relation, :name, :alias, :ancestor
@@ -67,9 +69,9 @@ module Arel
         !(history & other.history).empty?
       end
       
-      def %(other)
-        if other then (history - other.history) + (other.history - history)
-        else history
+      def /(other)
+        if other then (history & other.history).size.to_f / Set.new(history + other.history).size
+        else 0
         end
       end
     end
diff --git a/lib/arel/relations/join.rb b/lib/arel/relations/join.rb
index 4269731092..5356e57394 100644
--- a/lib/arel/relations/join.rb
+++ b/lib/arel/relations/join.rb
@@ -44,9 +44,12 @@ module Arel
     end
     
     def relation_for(attribute)
-      externalize([relation1[attribute], relation2[attribute]].select { |a| a =~ attribute }.min do |a1, a2|
-        (attribute % a1).size <=> (attribute % a2).size
-      end.relation).relation_for(attribute)
+      x = [externalize(relation1), externalize(relation2)].max do |r1, r2|
+        o1, o2 = r1.relation_for(attribute), r2.relation_for(attribute)
+        a1, a2 = o1 && o1[attribute], o2 && o2[attribute]
+        
+        attribute / a1 <=> attribute / a2
+      end.relation_for(attribute)
     end
     
     private
diff --git a/lib/arel/relations/nil.rb b/lib/arel/relations/nil.rb
index 258f60f478..b0d97dd174 100644
--- a/lib/arel/relations/nil.rb
+++ b/lib/arel/relations/nil.rb
@@ -2,6 +2,7 @@ module Arel
   class Nil < Relation
     def table; self end
     def table_sql(formatter = nil); '' end
+    def relation_for(attribute); nil end
     def name; '' end
     def to_s; '' end
     
diff --git a/lib/arel/relations/relation.rb b/lib/arel/relations/relation.rb
index cc0f40ea17..8c56a0cdcc 100644
--- a/lib/arel/relations/relation.rb
+++ b/lib/arel/relations/relation.rb
@@ -140,8 +140,8 @@ module Arel
       end
 
       def attribute_for_attribute(attribute)
-        attributes.select { |a| a =~ attribute }.min do |a1, a2|
-          (attribute % a1).size <=> (attribute % a2).size
+        attributes.select { |a| a =~ attribute }.max do |a1, a2|
+          (attribute / a1) <=> (attribute / a2)
         end
       end
     end