def instance_method_already_implemented?(method_name)
method_name = method_name.to_s
index = ancestors.index(ActiveRecord::Base) || ancestors.length
@_defined_class_methods ||= ancestors.first(index).map { |m|
m.instance_methods(false) | m.private_instance_methods(false)
}.flatten.map {|m| m.to_s }.to_set
@@_defined_activerecord_methods ||= defined_activerecord_methods
raise DangerousAttributeError, "#{method_name} is defined by ActiveRecord" if @@_defined_activerecord_methods.include?(method_name)
@_defined_class_methods.include?(method_name)
end