instance_method_already_implemented?

# File activerecord/lib/active_record/attribute_methods.rb, line 89
      def instance_method_already_implemented?(method_name)
        if dangerous_attribute_method?(method_name)
          raise DangerousAttributeError, "#{method_name} is defined by ActiveRecord"
        end

        if superclass == Base
          super
        else
          # If B < A and A defines its own attribute method, then we don't want to overwrite that.
          defined = method_defined_within?(method_name, superclass, superclass.generated_attribute_methods)
          defined && !ActiveRecord::Base.method_defined?(method_name) || super
        end
      end