belongs_to polymorphic association assignments update the foreign_id …

…and foreign_type fields regardless of whether the record being assigned is new or not.

fixes the following scenarios:
* I have validates_inclusion_of on the type field for a polymorphic belongs_to association.  I assign a new record to the model's polymorphic relationship of the proper type.  validation fails because the type field has not been updated.

* I replace the value for a ppolymorphic association to a new record of another class.  The type field still says its the previous class, and the id field points to the previous record as well.

activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb

@@ -7,10 +7,8 @@ def replace(record)
         else
           @target = (AssociationProxy === record ? record.target : record)
 
-          unless record.new_record?
-            @owner[@reflection.primary_key_name] = record.id
-            @owner[@reflection.options[:foreign_type]] = record.class.base_class.name.to_s
-          end
+          @owner[@reflection.primary_key_name] = record.id
+          @owner[@reflection.options[:foreign_type]] = record.class.base_class.name.to_s
 
           @updated = true
         end

activerecord/test/cases/associations/belongs_to_associations_test.rb

@@ -12,6 +12,8 @@
 require 'models/tag'
 require 'models/tagging'
 require 'models/comment'
+require 'models/sponsor'
+require 'models/member'
 
 class BelongsToAssociationsTest < ActiveRecord::TestCase
   fixtures :accounts, :companies, :developers, :projects, :topics,
@@ -381,5 +383,30 @@ def test_cant_save_readonly_association
     assert_raise(ActiveRecord::ReadOnlyRecord) { companies(:first_client).readonly_firm.save! }
     assert companies(:first_client).readonly_firm.readonly?
   end
-
+
+  def test_polymorphic_assignment_foreign_type_field_updating
+    # should update when assigning a saved record
+    sponsor = Sponsor.new
+    member = Member.create
+    sponsor.sponsorable = member
+    assert_equal "Member", sponsor.sponsorable_type
+
+    # should update when assigning a new record
+    sponsor = Sponsor.new
+    member = Member.new
+    sponsor.sponsorable = member
+    assert_equal "Member", sponsor.sponsorable_type
+  end
+
+  def test_polymorphic_assignment_updates_foreign_id_field_for_new_and_saved_records
+    sponsor = Sponsor.new
+    saved_member = Member.create
+    new_member = Member.new
+
+    sponsor.sponsorable = saved_member
+    assert_equal saved_member.id, sponsor.sponsorable_id
+
+    sponsor.sponsorable = new_member
+    assert_equal nil, sponsor.sponsorable_id
+  end
 end