5 files changed, 22 insertions, 5 deletions
diff --git a/activemodel/CHANGELOG.md b/activemodel/CHANGELOG.md
index 6f09c1cb43..2cb51945fd 100644
--- a/activemodel/CHANGELOG.md
+++ b/activemodel/CHANGELOG.md
@@ -1,3 +1,7 @@
+## Rails 3.2.11 (unreleased) ##
+
+*   Specify type of singular association during serialization *Steve Klabnik*
+
 ## Rails 3.2.10 ##
 
 ## Rails 3.2.9 (Nov 12, 2012) ##
diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index 00bd68512b..7eaee050cd 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -84,7 +84,7 @@ module ActiveModel
     end
 
     # Backport dup from 1.9 so that #initialize_dup gets called
-    unless Object.respond_to?(:initialize_dup)
+    unless Object.respond_to?(:initialize_dup, true)
       def dup # :nodoc:
         copy = super
         copy.initialize_dup(self)
diff --git a/activemodel/lib/active_model/serializers/xml.rb b/activemodel/lib/active_model/serializers/xml.rb
index 2dc7d00f52..a63856045f 100644
--- a/activemodel/lib/active_model/serializers/xml.rb
+++ b/activemodel/lib/active_model/serializers/xml.rb
@@ -144,7 +144,12 @@ module ActiveModel
             end
           else
             merged_options[:root] = association.to_s
-            records.to_xml(merged_options)
+
+            unless records.class.to_s.underscore == association.to_s
+              merged_options[:type] = records.class.name
+            end
+
+            records.to_xml merged_options
           end
         end
 
diff --git a/activemodel/lib/active_model/validations.rb b/activemodel/lib/active_model/validations.rb
index 45d8677fa0..c7e508958b 100644
--- a/activemodel/lib/active_model/validations.rb
+++ b/activemodel/lib/active_model/validations.rb
@@ -173,7 +173,7 @@ module ActiveModel
     end
 
     # Backport dup from 1.9 so that #initialize_dup gets called
-    unless Object.respond_to?(:initialize_dup)
+    unless Object.respond_to?(:initialize_dup, true)
       def dup # :nodoc:
         copy = super
         copy.initialize_dup(self)
diff --git a/activemodel/test/cases/serializers/xml_serialization_test.rb b/activemodel/test/cases/serializers/xml_serialization_test.rb
index 83db8d21f4..62c2b2035f 100644
--- a/activemodel/test/cases/serializers/xml_serialization_test.rb
+++ b/activemodel/test/cases/serializers/xml_serialization_test.rb
@@ -6,12 +6,12 @@ require 'ostruct'
 class Contact
   include ActiveModel::Serializers::Xml
 
-  attr_accessor :address, :friends
+  attr_accessor :address, :friends, :contact
 
   remove_method :attributes if method_defined?(:attributes)
 
   def attributes
-    instance_values.except("address", "friends")
+    instance_values.except("address", "friends", "contact")
   end
 end
 
@@ -55,6 +55,9 @@ class XmlSerializationTest < ActiveModel::TestCase
     @contact.address.state = "CA"
     @contact.address.zip = 11111
     @contact.friends = [Contact.new, Contact.new]
+    @related_contact = SerializableContact.new
+    @related_contact.name = "related"
+    @contact.contact = @related_contact
   end
 
   test "should serialize default root" do
@@ -203,4 +206,9 @@ class XmlSerializationTest < ActiveModel::TestCase
     assert_match %r{<friends>}, xml
     assert_match %r{<friend>}, xml
   end
+
+  test "association with sti" do
+    xml = @contact.to_xml(:include => :contact)
+    assert xml.include?(%(<contact type="SerializableContact">))
+  end
 end