diff --git a/lib/couchrest.rb b/lib/couchrest.rb
index 75459d1..02a6fe2 100644
--- a/lib/couchrest.rb
+++ b/lib/couchrest.rb
@@ -46,6 +46,7 @@ module CouchRest
   autoload :CastedModel,          'couchrest/more/casted_model'
   
   require File.join(File.dirname(__FILE__), 'couchrest', 'mixins')
+  require File.join(File.dirname(__FILE__), 'couchrest', 'support', 'rails')
   
   # The CouchRest module methods handle the basic JSON serialization 
   # and deserialization, as well as query parameters. The module also includes
diff --git a/lib/couchrest/mixins/properties.rb b/lib/couchrest/mixins/properties.rb
index 953e125..bc83571 100644
--- a/lib/couchrest/mixins/properties.rb
+++ b/lib/couchrest/mixins/properties.rb
@@ -37,37 +37,55 @@ module CouchRest
       def cast_keys
         return unless self.class.properties
         self.class.properties.each do |property|
-          next unless property.casted
-          key = self.has_key?(property.name) ? property.name : property.name.to_sym
-          # Don't cast the property unless it has a value
-          next unless self[key]
-          target = property.type
-          if target.is_a?(Array)
-            klass = ::CouchRest.constantize(target[0])
-            arr = self[key].collect do |value|
-              # Auto parse Time objects
-              obj = ( (property.init_method == 'new') && klass == Time) ? Time.parse(value) : klass.send(property.init_method, value)
-              obj.casted_by = self if obj.respond_to?(:casted_by)
-              obj.document_saved = true if obj.respond_to?(:document_saved)
-              obj
-            end
-            self[property.name] = target[0] != 'String' ? CastedArray.new(arr) : arr
-          else
-            # Auto parse Time objects
-            self[property.name] = if ((property.init_method == 'new') && target == 'Time') 
-              self[key].is_a?(String) ? Time.parse(self[key].dup) : self[key]
-            else
-              # Let people use :send as a Time parse arg
-              klass = ::CouchRest.constantize(target)
-              klass.send(property.init_method, self[key].dup)
-            end
-            self[property.name].casted_by = self if self[property.name].respond_to?(:casted_by)
-            self[property.name].document_saved = true if self[property.name].respond_to?(:document_saved)
-          end
-          self[property.name].casted_by = self if self[property.name].respond_to?(:casted_by)
+          cast_property(property)
         end
       end
       
+      def cast_property(property)
+        return unless property.casted
+        key = self.has_key?(property.name) ? property.name : property.name.to_sym
+        # Don't cast the property unless it has a value
+        return unless self[key]
+        target = property.type
+        if target.is_a?(Array)
+          klass = ::CouchRest.constantize(target[0])
+          arr = self[key].dup.collect do |value|
+            unless value.instance_of?(klass)
+              value = convert_property_value(property, klass, value)
+            end
+            associate_casted_to_parent(value)
+            value
+          end
+          self[key] = target[0] != 'String' ? CastedArray.new(arr) : arr
+        else
+          klass = ::CouchRest.constantize(target)
+          unless self[key].instance_of?(klass)
+            self[key] = convert_property_value(property, klass, self[property.name])
+          end
+          associate_casted_to_parent(self[property.name])
+        end
+      end
+      
+      def associate_casted_to_parent(casted)
+        casted.casted_by = self if casted.respond_to?(:casted_by)
+        casted.document_saved = true if casted.respond_to?(:document_saved)
+      end
+      
+      def convert_property_value(property, klass, value)
+        if ((property.init_method == 'new') && klass.to_s == 'Time') 
+          value.is_a?(String) ? Time.parse(value.dup) : value
+        else
+          klass.send(property.init_method, value.dup)
+        end
+      end
+      
+      def cast_property_by_name(property_name)
+        return unless self.class.properties
+        property = self.class.properties.detect{|property| property.name == property_name}
+        return unless property
+        cast_property(property)
+      end
+      
       module ClassMethods
         
         def property(name, options={})
@@ -108,24 +126,17 @@ module CouchRest
 
           # defines the setter for the property (and optional aliases)
           def create_property_setter(property)
-            meth = property.name
+            property_name = property.name
             class_eval <<-EOS
-              def #{meth}=(value)
-                if #{property.casted} && value.is_a?(Array)
-                  arr = CastedArray.new
-                  arr.casted_by = self
-                  value.each { |v| arr << v }
-                  value = arr
-                elsif #{property.casted}
-                  value.casted_by = self if value.respond_to?(:casted_by)
-                end
-                self['#{meth}'] = value
+              def #{property_name}=(value)
+                self['#{property_name}'] = value
+                cast_property_by_name('#{property_name}')
               end
             EOS
 
             if property.alias
               class_eval <<-EOS
-                alias #{property.alias.to_sym}= #{meth.to_sym}=
+                alias #{property.alias.to_sym}= #{property_name.to_sym}=
               EOS
             end
           end
diff --git a/lib/couchrest/more/extended_document.rb b/lib/couchrest/more/extended_document.rb
index 44c73c3..a3e941b 100644
--- a/lib/couchrest/more/extended_document.rb
+++ b/lib/couchrest/more/extended_document.rb
@@ -51,9 +51,6 @@ module CouchRest
       end
     end
     
-
-    
-    
     # Automatically set <tt>updated_at</tt> and <tt>created_at</tt> fields
     # on the document whenever saving occurs. CouchRest uses a pretty
     # decent time format by default. See Time#to_json
@@ -68,7 +65,7 @@ module CouchRest
         end
       EOS
     end
-  
+    
     # Name a method that will be called before the document is first saved,
     # which returns a string to be used for the document's <tt>_id</tt>.
     # Because CouchDB enforces a constraint that each id must be unique,
@@ -127,10 +124,15 @@ module CouchRest
     # for each key. It doesn't save the document at the end. Raises a NoMethodError if the corresponding methods are
     # missing. In case of error, no attributes are changed.    
     def update_attributes_without_saving(hash)
-      hash.each do |k, v|
+      # remove attributes that cannot be updated, silently ignoring them
+      # which matches Rails behavior when, for instance, setting created_at.
+      # make a copy, we don't want to change arguments
+      attrs = hash.dup
+      %w[_id _rev created_at updated_at].each {|attr| attrs.delete(attr)}
+      attrs.each do |k, v|
         raise NoMethodError, "#{k}= method not available, use property :#{k}" unless self.respond_to?("#{k}=")
       end      
-      hash.each do |k, v|
+      attrs.each do |k, v|
         self.send("#{k}=",v)
       end
     end
diff --git a/lib/couchrest/support/rails.rb b/lib/couchrest/support/rails.rb
index 2fa267c..41957d4 100644
--- a/lib/couchrest/support/rails.rb
+++ b/lib/couchrest/support/rails.rb
@@ -1,52 +1,53 @@
 # This file contains various hacks for Rails compatibility.
-# To use, just require in environment.rb, like so:
-#
-#   require 'couchrest/support/rails'
 
-class Hash
-  # Hack so that CouchRest::Document, which descends from Hash,
-  # doesn't appear to Rails routing as a Hash of options
-  def self.===(other)
-    return false if self == Hash && other.is_a?(CouchRest::Document)
-    super
+if defined?(Rails)
+
+  class Hash
+    # Hack so that CouchRest::Document, which descends from Hash,
+    # doesn't appear to Rails routing as a Hash of options
+    def self.===(other)
+      return false if self == Hash && other.is_a?(CouchRest::Document)
+      super
+    end
   end
-end
 
 
-CouchRest::Document.class_eval do
-  # Need this when passing doc to a resourceful route
-  alias_method :to_param, :id
+  CouchRest::Document.class_eval do
+    # Need this when passing doc to a resourceful route
+    alias_method :to_param, :id
   
-  # Hack so that CouchRest::Document, which descends from Hash,
-  # doesn't appear to Rails routing as a Hash of options
-  def is_a?(o)
-    return false if o == Hash
-    super
-  end
-  alias_method :kind_of?, :is_a?
+    # Hack so that CouchRest::Document, which descends from Hash,
+    # doesn't appear to Rails routing as a Hash of options
+    def is_a?(o)
+      return false if o == Hash
+      super
+    end
+    alias_method :kind_of?, :is_a?
   
-  # Gives extended doc a seamless logger
-  def logger
-    ActiveRecord::Base.logger
+    # Gives extended doc a seamless logger
+    def logger
+      ActiveRecord::Base.logger
+    end
   end
-end
 
-CouchRest::CastedModel.class_eval do
-  # The to_param method is needed for rails to generate resourceful routes.
-  # In your controller, remember that it's actually the id of the document.
-  def id
-    return nil if base_doc.nil?
-    base_doc.id
+  CouchRest::CastedModel.class_eval do
+    # The to_param method is needed for rails to generate resourceful routes.
+    # In your controller, remember that it's actually the id of the document.
+    def id
+      return nil if base_doc.nil?
+      base_doc.id
+    end
+    alias_method :to_param, :id
   end
-  alias_method :to_param, :id
-end
 
-require Pathname.new(File.dirname(__FILE__)).join('..', 'validation', 'validation_errors')
+  require Pathname.new(File.dirname(__FILE__)).join('..', 'validation', 'validation_errors')
 
-CouchRest::Validation::ValidationErrors.class_eval do
-  # Returns the total number of errors added. Two errors added to the same attribute will be counted as such.
-  # This method is called by error_messages_for
-  def count
-    errors.values.inject(0) { |error_count, errors_for_attribute| error_count + errors_for_attribute.size }
+  CouchRest::Validation::ValidationErrors.class_eval do
+    # Returns the total number of errors added. Two errors added to the same attribute will be counted as such.
+    # This method is called by error_messages_for
+    def count
+      errors.values.inject(0) { |error_count, errors_for_attribute| error_count + errors_for_attribute.size }
+    end
   end
-end
+
+end
\ No newline at end of file
diff --git a/spec/couchrest/more/casted_extended_doc_spec.rb b/spec/couchrest/more/casted_extended_doc_spec.rb
index 51afd77..eef1541 100644
--- a/spec/couchrest/more/casted_extended_doc_spec.rb
+++ b/spec/couchrest/more/casted_extended_doc_spec.rb
@@ -43,16 +43,14 @@ describe "assigning a value to casted attribute after initializing an object" do
     @car.driver.should be_nil
   end
   
-  # Note that this isn't casting the attribute, it's just assigning it a value
-  # (see "should not cast attribute")
   it "should let you assign the value" do
     @car.driver = @driver
     @car.driver.name.should == 'Matt'
   end
   
-  it "should not cast attribute" do
+  it "should cast attribute" do
     @car.driver = JSON.parse(JSON.generate(@driver))
-    @car.driver.should_not be_instance_of(Driver)
+    @car.driver.should be_instance_of(Driver)
   end
 
 end
diff --git a/spec/couchrest/more/casted_model_spec.rb b/spec/couchrest/more/casted_model_spec.rb
index a1bbc43..293a66e 100644
--- a/spec/couchrest/more/casted_model_spec.rb
+++ b/spec/couchrest/more/casted_model_spec.rb
@@ -288,7 +288,8 @@ describe CouchRest::CastedModel do
     before :each do
       reset_test_db!
       @cat = Cat.new(:name => 'Sockington')
-      @cat.favorite_toy = CatToy.new(:name => 'Catnip Ball')
+      @favorite_toy = CatToy.new(:name => 'Catnip Ball')
+      @cat.favorite_toy = @favorite_toy
       @cat.toys << CatToy.new(:name => 'Fuzzy Stick')
     end
     
@@ -298,6 +299,7 @@ describe CouchRest::CastedModel do
     end
     
     it "should be true after assignment" do
+      @cat.should be_new
       @cat.favorite_toy.should be_new
       @cat.toys.first.should be_new
     end
@@ -340,6 +342,7 @@ describe CouchRest::CastedModel do
     
     it "should reference the top document for" do
       @course.base_doc.should === @course
+      @professor.casted_by.should === @course
       @professor.base_doc.should === @course
       @cat.base_doc.should === @course
       @toy1.base_doc.should === @course
@@ -347,6 +350,7 @@ describe CouchRest::CastedModel do
     end
     
     it "should call setter on top document" do
+      @toy1.base_doc.should_not be_nil
       @toy1.base_doc.title = 'Tom Foolery'
       @course.title.should == 'Tom Foolery'
     end
diff --git a/spec/couchrest/more/extended_doc_spec.rb b/spec/couchrest/more/extended_doc_spec.rb
index d4100bf..403eedd 100644
--- a/spec/couchrest/more/extended_doc_spec.rb
+++ b/spec/couchrest/more/extended_doc_spec.rb
@@ -118,7 +118,22 @@ describe "ExtendedDocument" do
       @art.update_attributes_without_saving('date' => Time.now, :title => "super danger")
       @art['title'].should == "super danger"
     end
-    
+    it "should silently ignore _id" do
+      @art.update_attributes_without_saving('_id' => 'foobar')
+      @art['_id'].should_not == 'foobar'
+    end
+    it "should silently ignore _rev" do
+      @art.update_attributes_without_saving('_rev' => 'foobar')
+      @art['_rev'].should_not == 'foobar'
+    end
+    it "should silently ignore created_at" do
+      @art.update_attributes_without_saving('created_at' => 'foobar')
+      @art['created_at'].should_not == 'foobar'
+    end
+    it "should silently ignore updated_at" do
+      @art.update_attributes_without_saving('updated_at' => 'foobar')
+      @art['updated_at'].should_not == 'foobar'
+    end
     it "should also work using attributes= alias" do
       @art.respond_to?(:attributes=).should be_true
       @art.attributes = {'date' => Time.now, :title => "something else"}