6 files changed, 24 insertions, 4 deletions
diff --git a/activerecord/CHANGELOG b/activerecord/CHANGELOG
index 1a287ec7d8..c3bae2c841 100644
--- a/activerecord/CHANGELOG
+++ b/activerecord/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Polymorphic join support for has_one associations (has_one :foo, :as => :bar)  #3785 [Rick Olson]
+
 * PostgreSQL: correctly parse negative integer column defaults.  #3776 [bellis@deepthought.org]
 
 * Fix problems with count when used with :include [Jeremy Hopple and Kevin Clark]
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 6b461b5514..0dc03487cb 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -899,7 +899,7 @@ module ActiveRecord
 
         def create_has_one_reflection(association_id, options)
           options.assert_valid_keys(
-            :class_name, :foreign_key, :remote, :conditions, :order, :include, :dependent, :counter_cache, :extend
+            :class_name, :foreign_key, :remote, :conditions, :order, :include, :dependent, :counter_cache, :extend, :as
           )
 
           reflection = create_reflection(:has_one, association_id, options, self)
diff --git a/activerecord/lib/active_record/associations/has_one_association.rb b/activerecord/lib/active_record/associations/has_one_association.rb
index 17483305fc..4dbc0f6441 100644
--- a/activerecord/lib/active_record/associations/has_one_association.rb
+++ b/activerecord/lib/active_record/associations/has_one_association.rb
@@ -66,9 +66,15 @@ module ActiveRecord
         end
 
         def construct_sql
-          @finder_sql = "#{@reflection.table_name}.#{@reflection.primary_key_name} = #{@owner.quoted_id}"
+          case
+            when @reflection.options[:as]
+              @finder_sql = 
+                "#{@reflection.klass.table_name}.#{@reflection.options[:as]}_id = #{@owner.quoted_id} AND " + 
+                "#{@reflection.klass.table_name}.#{@reflection.options[:as]}_type = '#{ActiveRecord::Base.send(:class_name_of_active_record_descendant, @owner.class).to_s}'"          
+            else
+              @finder_sql = "#{@reflection.table_name}.#{@reflection.primary_key_name} = #{@owner.quoted_id}"
+          end
           @finder_sql << " AND (#{sanitize_sql(@reflection.options[:conditions])})" if @reflection.options[:conditions]
-          @finder_sql
         end
     end
   end
diff --git a/activerecord/test/associations_join_model_test.rb b/activerecord/test/associations_join_model_test.rb
index 61488900d6..5437e049a3 100644
--- a/activerecord/test/associations_join_model_test.rb
+++ b/activerecord/test/associations_join_model_test.rb
@@ -26,6 +26,10 @@ class AssociationsJoinModelTest < Test::Unit::TestCase
   def test_polymorphic_has_many
     assert_equal taggings(:welcome_general), posts(:welcome).taggings.first
   end
+  
+  def test_polymorphic_has_one
+    assert_equal taggings(:welcome_general), posts(:welcome).tagging
+  end
 
   def test_polymorphic_belongs_to
     assert_equal posts(:welcome), posts(:welcome).taggings.first.taggable
@@ -46,7 +50,12 @@ class AssociationsJoinModelTest < Test::Unit::TestCase
     tagging = tags(:misc).taggings.create(:taggable => post)
     assert_equal "Post", tagging.taggable_type
   end
-  
+
+  def test_polymorphic_has_one_create_model_with_inheritance
+    tagging = tags(:misc).create_tagging(:taggable => posts(:thinking))
+    assert_equal "Post", tagging.taggable_type
+  end
+
   def test_has_many_with_piggyback
     assert_equal "2", categories(:sti_test).authors.first.post_id.to_s
   end
diff --git a/activerecord/test/fixtures/post.rb b/activerecord/test/fixtures/post.rb
index ada18af115..4c2ccb3f43 100644
--- a/activerecord/test/fixtures/post.rb
+++ b/activerecord/test/fixtures/post.rb
@@ -23,6 +23,8 @@ class Post < ActiveRecord::Base
   has_many :taggings, :as => :taggable
   has_many :tags, :through => :taggings
 
+  has_one :tagging, :as => :taggable
+
   has_many :categorizations, :foreign_key => :category_id
   has_many :authors, :through => :categorizations
 
diff --git a/activerecord/test/fixtures/tag.rb b/activerecord/test/fixtures/tag.rb
index d54f3cd680..78b6f6666c 100644
--- a/activerecord/test/fixtures/tag.rb
+++ b/activerecord/test/fixtures/tag.rb
@@ -1,3 +1,4 @@
 class Tag < ActiveRecord::Base
   has_many :taggings, :as => :taggable
+  has_one  :tagging,  :as => :taggable
 end
 \ No newline at end of file