path: root/activerecord/lib/active_record/attribute_methods/read.rb

module ActiveRecord
  module AttributeMethods
    module Read
      extend ActiveSupport::Concern

      ATTRIBUTE_TYPES_CACHED_BY_DEFAULT = [:datetime, :timestamp, :time, :date]

      included do
        attribute_method_suffix ""

        cattr_accessor :attribute_types_cached_by_default, :instance_writer => false
        self.attribute_types_cached_by_default = ATTRIBUTE_TYPES_CACHED_BY_DEFAULT

        # Undefine id so it can be used as an attribute name
        undef_method(:id) if method_defined?(:id)
      end

      module ClassMethods
        # +cache_attributes+ allows you to declare which converted attribute values should
        # be cached. Usually caching only pays off for attributes with expensive conversion
        # methods, like time related columns (e.g. +created_at+, +updated_at+).
        def cache_attributes(*attribute_names)
          cached_attributes.merge attribute_names.map { |attr| attr.to_s }
        end

        # Returns the attributes which are cached. By default time related columns
        # with datatype <tt>:datetime, :timestamp, :time, :date</tt> are cached.
        def cached_attributes
          @cached_attributes ||= columns.select { |c| cacheable_column?(c) }.map { |col| col.name }.to_set
        end

        # Returns +true+ if the provided attribute is being cached.
        def cache_attribute?(attr_name)
          cached_attributes.include?(attr_name)
        end

        protected
          def define_method_attribute(attr_name)
            if serialized_attributes.include?(attr_name)
              define_read_method_for_serialized_attribute(attr_name)
            else
              define_read_method(attr_name, attr_name, columns_hash[attr_name])
            end

            if attr_name == primary_key && attr_name != "id"
              define_read_method(:id, attr_name, columns_hash[attr_name])
            end
          end

        private
          def cacheable_column?(column)
            serialized_attributes.include?(column.name) || attribute_types_cached_by_default.include?(column.type)
          end

          # Define read method for serialized attribute.
          def define_read_method_for_serialized_attribute(attr_name)
            access_code = "@attributes_cache['#{attr_name}'] ||= @attributes['#{attr_name}']"
            generated_attribute_methods.module_eval("def _#{attr_name}; #{access_code}; end; alias #{attr_name} _#{attr_name}", __FILE__, __LINE__)
          end

          # Define an attribute reader method.  Cope with nil column.
          def define_read_method(symbol, 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
            if symbol =~ /^[a-zA-Z_]\w*[!?=]?$/
              generated_attribute_methods.module_eval("def _#{symbol}; #{access_code}; end; alias #{symbol} _#{symbol}", __FILE__, __LINE__)
            else
              generated_attribute_methods.module_eval do
                define_method("_#{symbol}") { eval(access_code) }
                alias_method(symbol, "_#{symbol}")
              end
            end
          end
      end

      # Returns the value of the attribute identified by <tt>attr_name</tt> after it has been typecast (for example,
      # "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)).
      def read_attribute(attr_name)
        send "_#{attr_name}"
      rescue NoMethodError
        _read_attribute attr_name
      end

      def _read_attribute(attr_name)
        attr_name = attr_name.to_s
        attr_name = self.class.primary_key if attr_name == 'id'
        value = @attributes[attr_name]
        unless value.nil?
          if column = column_for_attribute(attr_name)
            if unserializable_attribute?(attr_name, column)
              unserialize_attribute(attr_name)
            else
              column.type_cast(value)
            end
          else
            value
          end
        end
      end

      # Returns true if the attribute is of a text column and marked for serialization.
      def unserializable_attribute?(attr_name, column)
        column.text? && self.class.serialized_attributes.include?(attr_name)
      end

      # Returns the unserialized object of the attribute.
      def unserialize_attribute(attr_name)
        coder = self.class.serialized_attributes[attr_name]
        unserialized_object = coder.load(@attributes[attr_name])

        @attributes.frozen? ? unserialized_object : @attributes[attr_name] = unserialized_object
      end

      private
        def attribute(attribute_name)
          read_attribute(attribute_name)
        end
    end
  end
end