From 0b5a91673ee74ca6e1acbbfd53362a05de0b5907 Mon Sep 17 00:00:00 2001
From: Ryan Aipperspach <ryan@goodguide.com>
Date: Thu, 7 Apr 2011 13:39:12 -0700
Subject: [PATCH] Put conditions for polymorphic joins in the ON instead of WHERE clause, in order to support OUTER JOINs

---
 .../associations/association_scope.rb              |    4 +++-
 .../join_dependency/join_association.rb            |    1 +
 .../lib/active_record/associations/join_helper.rb  |   15 +++++++++++++++
 activerecord/lib/active_record/reflection.rb       |    4 ----
 .../test/cases/associations/join_model_test.rb     |   15 +++++++++++++++
 5 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/activerecord/lib/active_record/associations/association_scope.rb b/activerecord/lib/active_record/associations/association_scope.rb
index ab102b2..8fdb92b 100644
--- a/activerecord/lib/active_record/associations/association_scope.rb
+++ b/activerecord/lib/active_record/associations/association_scope.rb
@@ -87,7 +87,9 @@ module ActiveRecord
             end
           else
             constraint = table[key].eq(foreign_table[foreign_key])
-            join       = join(foreign_table, constraint)
+            constraint = append_source_type_condition(constraint, table, foreign_table, reflection)
+            
+            join = join(foreign_table, constraint)
 
             scope = scope.joins(join)
 
diff --git a/activerecord/lib/active_record/associations/join_dependency/join_association.rb b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
index 4121a5b..f44efb2 100644
--- a/activerecord/lib/active_record/associations/join_dependency/join_association.rb
+++ b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
@@ -90,6 +90,7 @@ module ActiveRecord
             end
 
             constraint = table[key].eq(foreign_table[foreign_key])
+            constraint = append_source_type_condition(constraint, table, foreign_table, reflection)
 
             if reflection.klass.finder_needs_type_condition?
               constraint = table.create_and([
diff --git a/activerecord/lib/active_record/associations/join_helper.rb b/activerecord/lib/active_record/associations/join_helper.rb
index eae546e..9f56b5a 100644
--- a/activerecord/lib/active_record/associations/join_helper.rb
+++ b/activerecord/lib/active_record/associations/join_helper.rb
@@ -26,6 +26,21 @@ module ActiveRecord
         end
         tables
       end
+      
+      def append_source_type_condition(constraint, table, foreign_table, reflection)
+        source_type = reflection.options[:source_type] ||
+          (reflection.source_reflection && 
+           reflection.source_reflection.options[:source_type])
+        
+        if (source_type)
+          table.create_and([
+            constraint,
+            foreign_table[reflection.foreign_type].eq(source_type)
+          ])
+        else
+          constraint
+        end
+      end
 
       def table_name_for(reflection)
         reflection.table_name
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index e801bc4..339ceae 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -450,10 +450,6 @@ module ActiveRecord
 
           through_conditions = through_reflection.conditions
 
-          if options[:source_type]
-            through_conditions.first << { foreign_type => options[:source_type] }
-          end
-
           # Recursively fill out the rest of the array from the through reflection
           conditions += through_conditions
 
diff --git a/activerecord/test/cases/associations/join_model_test.rb b/activerecord/test/cases/associations/join_model_test.rb
index 5a7b139..d01544d 100644
--- a/activerecord/test/cases/associations/join_model_test.rb
+++ b/activerecord/test/cases/associations/join_model_test.rb
@@ -362,6 +362,21 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
     end
     assert_equal 5, tag_with_include.taggings.length
   end
+  
+  def test_has_many_polymporphic_with_source_type_and_some_empty_children
+    tags(:misc).taggings.destroy_all
+    tags(:blue).taggings.destroy_all
+
+    assert tags(:general).taggings.present?
+    assert tags(:misc).taggings.empty?
+    assert tags(:blue).taggings.empty?
+    
+    tags_without_taggings = Tag.includes(:tagged_posts).where(:taggings => {:id => nil}).limit(100).all
+    
+    desired = tags(:misc, :blue)
+    
+    assert_equal desired.sort_by(&:id), tags_without_taggings.sort_by(&:id)
+  end
 
   def test_has_many_through_has_many_find_all
     assert_equal comments(:greetings), authors(:david).comments.find(:all, :order => 'comments.id').first
-- 
1.6.5.1