diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 6931744..c049950 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1109,6 +1109,8 @@ module ActiveRecord
               association = association_proxy_class.new(self, reflection)
             end
 
+            new_value = reflection.klass.new(new_value) if reflection.options[:accessible] && new_value.is_a?(Hash)
+
             if association_proxy_class == HasOneThroughAssociation
               association.create_through_record(new_value)
               self.send(reflection.name, new_value)
@@ -1357,7 +1359,7 @@ module ActiveRecord
             :finder_sql, :counter_sql,
             :before_add, :after_add, :before_remove, :after_remove,
             :extend, :readonly,
-            :validate
+            :validate, :accessible
           )
 
           options[:extend] = create_extension_modules(association_id, extension, options[:extend])
@@ -1367,7 +1369,7 @@ module ActiveRecord
 
         def create_has_one_reflection(association_id, options)
           options.assert_valid_keys(
-            :class_name, :foreign_key, :remote, :select, :conditions, :order, :include, :dependent, :counter_cache, :extend, :as, :readonly, :validate, :primary_key
+            :class_name, :foreign_key, :remote, :select, :conditions, :order, :include, :dependent, :counter_cache, :extend, :as, :readonly, :validate, :primary_key, :accessible
           )
 
           create_reflection(:has_one, association_id, options, self)
diff --git a/activerecord/lib/active_record/associations/association_collection.rb b/activerecord/lib/active_record/associations/association_collection.rb
index eb39714..a8db8d8 100644
--- a/activerecord/lib/active_record/associations/association_collection.rb
+++ b/activerecord/lib/active_record/associations/association_collection.rb
@@ -94,6 +94,8 @@ module ActiveRecord
 
         @owner.transaction do
           flatten_deeper(records).each do |record|
+            record = @reflection.klass.new(record) if @reflection.options[:accessible] && record.is_a?(Hash)
+
             raise_on_type_mismatch(record)
             add_record_to_target_with_callbacks(record) do |r|
               result &&= insert_record(record) unless @owner.new_record?
@@ -226,6 +228,10 @@ module ActiveRecord
       # Replace this collection with +other_array+
       # This will perform a diff and delete/add only records that have changed.
       def replace(other_array)
+        other_array.map! do |val|
+          val.is_a?(Hash) ? @reflection.klass.new(val) : val
+        end if @reflection.options[:accessible]
+
         other_array.each { |val| raise_on_type_mismatch(val) }
 
         load_target
diff --git a/activerecord/test/cases/associations/belongs_to_associations_test.rb b/activerecord/test/cases/associations/belongs_to_associations_test.rb
index 9c718c4..daa8430 100755
--- a/activerecord/test/cases/associations/belongs_to_associations_test.rb
+++ b/activerecord/test/cases/associations/belongs_to_associations_test.rb
@@ -40,6 +40,14 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_raise(ActiveRecord::AssociationTypeMismatch) { Account.find(1).firm = Project.find(1) }
   end
 
+  def test_belongs_to_mass_assignment
+    assert_no_difference 'Firm.count' do
+      assert_raise(ActiveRecord::AssociationTypeMismatch) do
+        Account.create(:credit_limit => 10, :firm => { :name => 'Apple' })
+      end
+    end
+  end
+
   def test_natural_assignment
     apple = Firm.create("name" => "Apple")
     citibank = Account.create("credit_limit" => 10)
diff --git a/activerecord/test/cases/associations_test.rb b/activerecord/test/cases/associations_test.rb
index 59349dd..80bbac7 100755
--- a/activerecord/test/cases/associations_test.rb
+++ b/activerecord/test/cases/associations_test.rb
@@ -189,6 +189,26 @@ class AssociationProxyTest < ActiveRecord::TestCase
     end
   end
 
+  def test_association_proxy_setter_can_take_hash
+    special_comment_attributes = { :body => 'Setter Takes Hash' }
+
+    post = posts(:welcome)
+    post.creatable_comment = { :body => 'Setter Takes Hash' }
+
+    assert_equal post.creatable_comment.body, special_comment_attributes[:body]
+  end
+
+  def test_association_collection_can_take_hash
+    post_attributes = { :title => 'Setter Takes', :body => 'Hash' }
+    david = authors(:david)
+
+    post = (david.posts << post_attributes).last
+    assert_equal post.title, post_attributes[:title]
+
+    david.posts = [post_attributes, post_attributes]
+    assert_equal david.posts.count, 2
+  end
+
   def setup_dangling_association
     josh = Author.create(:name => "Josh")
     p = Post.create(:title => "New on Edge", :body => "More cool stuff!", :author => josh)
diff --git a/activerecord/test/cases/base_test.rb b/activerecord/test/cases/base_test.rb
index a4be629..448e31b 100755
--- a/activerecord/test/cases/base_test.rb
+++ b/activerecord/test/cases/base_test.rb
@@ -62,6 +62,11 @@ class ReadonlyTitlePost < Post
   attr_readonly :title
 end
 
+class Jedi < LoosePerson
+  has_one :father
+  has_one :mentor, :accessible => true
+end
+
 class Booleantest < ActiveRecord::Base; end
 
 class Task < ActiveRecord::Base
diff --git a/activerecord/test/models/author.rb b/activerecord/test/models/author.rb
index 82e0690..136dc39 100644
--- a/activerecord/test/models/author.rb
+++ b/activerecord/test/models/author.rb
@@ -1,5 +1,5 @@
 class Author < ActiveRecord::Base
-  has_many :posts
+  has_many :posts, :accessible => true
   has_many :posts_with_comments, :include => :comments, :class_name => "Post"
   has_many :posts_with_comments_sorted_by_comment_id, :include => :comments, :class_name => "Post", :order => 'comments.id'
   has_many :posts_with_categories, :include => :categories, :class_name => "Post"
diff --git a/activerecord/test/models/post.rb b/activerecord/test/models/post.rb
index 3adbc0c..f5d8d3a 100644
--- a/activerecord/test/models/post.rb
+++ b/activerecord/test/models/post.rb
@@ -30,6 +30,8 @@ class Post < ActiveRecord::Base
   has_many :special_comments
   has_many :nonexistant_comments, :class_name => 'Comment', :conditions => 'comments.id < 0'
 
+  has_one        :creatable_comment, :class_name => 'Comment', :accessible => true
+
   has_and_belongs_to_many :categories
   has_and_belongs_to_many :special_categories, :join_table => "categories_posts", :association_foreign_key => 'category_id'