ditto for id=

activerecord/lib/active_record/attribute_methods.rb

@@ -89,7 +89,7 @@ def undefine_attribute_methods
       # method is defined by Active Record though.
       def instance_method_already_implemented?(method_name)
         method_name = method_name.to_s
-        return true if method_name =~ /^id(=$|\?$|$)/
+        return true if method_name == "id"
         @_defined_class_methods         ||= ancestors.first(ancestors.index(ActiveRecord::Base)).sum([]) { |m| m.public_instance_methods(false) | m.private_instance_methods(false) | m.protected_instance_methods(false) }.map {|m| m.to_s }.to_set
         @@_defined_activerecord_methods ||= (ActiveRecord::Base.public_instance_methods(false) | ActiveRecord::Base.private_instance_methods(false) | ActiveRecord::Base.protected_instance_methods(false)).map{|m| m.to_s }.to_set
         raise DangerousAttributeError, "#{method_name} is defined by ActiveRecord" if @@_defined_activerecord_methods.include?(method_name)
@@ -152,7 +152,7 @@ def method_missing(method_id, *args, &block)
         id
       elsif md = self.class.match_attribute_method?(method_name)
         attribute_name, method_type = md.pre_match, md.to_s
-        if @attributes.include?(attribute_name)
+        if attribute_name == 'id' || @attributes.include?(attribute_name)
           __send__("attribute#{method_type}", attribute_name, *args, &block)
         else
           super
@@ -182,7 +182,7 @@ def respond_to?(method, include_private_methods = false)
       end
 
       if md = self.class.match_attribute_method?(method_name)
-        return true if @attributes.include?(md.pre_match)
+        return true if md.pre_match == 'id' || @attributes.include?(md.pre_match)
       end
       super
     end

activerecord/lib/active_record/attribute_methods/write.rb

@@ -18,6 +18,7 @@ def define_attribute_method=(attr_name)
       # columns are turned into +nil+.
       def write_attribute(attr_name, value)
         attr_name = attr_name.to_s
+        attr_name = self.class.primary_key if attr_name == 'id'
         @attributes_cache.delete(attr_name)
         if (column = column_for_attribute(attr_name)) && column.number?
           @attributes[attr_name] = convert_number_column_value(value)
@@ -26,11 +27,6 @@ def write_attribute(attr_name, value)
         end
       end
 
-      # Sets the primary ID.
-      def id=(value)
-        write_attribute(self.class.primary_key, value)
-      end
-
       private
         # Handle *= for method_missing.
         def attribute=(attribute_name, value)