instance method define_read_method

# File activerecord/lib/active_record/attribute_methods/read.rb, line 64
          def define_read_method(method_name, attr_name, column)
            cast_code = column.type_cast_code('v')
            access_code = "(v=@attributes['#{attr_name}']) && #{cast_code}"

            unless attr_name.to_s == self.primary_key.to_s
              access_code.insert(0, "missing_attribute('#{attr_name}', caller) unless @attributes.has_key?('#{attr_name}'); ")
            end

            if cache_attribute?(attr_name)
              access_code = "@attributes_cache['#{attr_name}'] ||= (#{access_code})"
            end

            # Where possible, generate the method by evalling a string, as this will result in
            # faster accesses because it avoids the block eval and then string eval incurred
            # by the second branch.
            #
            # The second, slower, branch is necessary to support instances where the database
            # returns columns with extra stuff in (like 'my_column(omg)').
            if method_name =~ ActiveModel::AttributeMethods::COMPILABLE_REGEXP
              generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__
                def _#{method_name}
                  #{access_code}
                end

                alias #{method_name} _#{method_name}
              STR
            else
              generated_attribute_methods.module_eval do
                define_method("_#{method_name}") { eval(access_code) }
                alias_method(method_name, "_#{method_name}")
              end
            end
          end