instance_method_already_implemented? (ActiveRecord::AttributeMethods::ClassMethods)

    # File lib/active_record/attribute_methods.rb, line 99
          def instance_method_already_implemented?(method_name)
            method_name = method_name.to_s
            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(&: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(&:to_s).to_set
            raise DangerousAttributeError, "#{method_name} is defined by ActiveRecord" if @@_defined_activerecord_methods.include?(method_name)
            @_defined_class_methods.include?(method_name)
          end