better column disambiguation

6 files changed, 60 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
diff --git a/spec/arel/unit/primitives/attribute_spec.rb b/spec/arel/unit/primitives/attribute_spec.rb
index 561c47da16..b253892b58 100644
--- a/spec/arel/unit/primitives/attribute_spec.rb
+++ b/spec/arel/unit/primitives/attribute_spec.rb
@@ -57,6 +57,35 @@ module Arel
         end
       end
       
+      describe '/' do
+        before do
+          @aliased_relation = @relation.alias
+          @doubly_aliased_relation = @aliased_relation.alias.alias.alias.alias
+        end
+        
+        describe 'when dividing two identical attributes' do
+          it "returns 1.0" do
+            (@relation[:id] / @relation[:id]).should == 1.0
+            (@aliased_relation[:id] / @aliased_relation[:id]).should == 1.0
+          end
+        end
+        
+        describe 'when dividing two unrelated attributes' do
+          it "returns 0.0" do
+            (@relation[:id] / @relation[:name]).should == 0.0
+          end
+        end
+        
+        describe 'when dividing two similar attributes' do
+          it 'returns a the highest score for the most similar attributes' do
+            (@aliased_relation[:id] / @relation[:id]) \
+              .should == (@aliased_relation[:id] / @relation[:id])
+            (@aliased_relation[:id] / @relation[:id]) \
+              .should < (@aliased_relation[:id] / @aliased_relation[:id])
+          end
+        end
+      end
+      
       describe 'hashing' do
         it "implements hash equality" do
           Attribute.new(@relation, 'name').should hash_the_same_as(Attribute.new(@relation, 'name'))
diff --git a/spec/arel/unit/relations/join_spec.rb b/spec/arel/unit/relations/join_spec.rb
index d517da8c1f..a538c8af68 100644
--- a/spec/arel/unit/relations/join_spec.rb
+++ b/spec/arel/unit/relations/join_spec.rb
@@ -203,6 +203,23 @@ module Arel
           end
         end
       end
+      
+      describe 'something really really complex' do
+        it '' do
+          users = @relation1
+          photos = @relation2
+          users_2 = users.alias
+          photos_2 = photos.alias
+          r = users \
+            .join(photos) \
+              .on(photos[:user_id].eq users[:id]) \
+            .join(users_2) \
+              .on(users_2[:id].eq photos[:user_id]) \
+            .join(photos_2) \
+              .on(users_2[:id].eq photos_2[:user_id])
+          r.relation_for(photos[:user_id]).should == photos
+        end
+      end
         
       describe '[]' do
         describe 'when given an attribute belonging to both sub-relations' do