# module ActiveModel::AttributeMethods::ClassMethods

### Public Instance Methods

alias_attribute(new_name, old_name) click to toggle source

Allows you to make aliases for attributes.

    class Person
      include ActiveModel::AttributeMethods

      attr_accessor :name
      attribute_method_suffix '_short?'
      define_attribute_methods :name

      alias_attribute :nickname, :name

      private

      def attribute_short?(attr)
        send(attr).length < 5
      end
    end

    person = Person.new
    person.name = 'Bob'
    person.name            # => "Bob"
    person.nickname        # => "Bob"
    person.name_short?     # => true
    person.nickname_short? # => true

    # File lib/active_model/attribute_methods.rb, line 208
    def alias_attribute(new_name, old_name)
      self.attribute_aliases = attribute_aliases.merge(new_name.to_s => old_name.to_s)
      attribute_method_matchers.each do |matcher|
        matcher_new = matcher.method_name(new_name).to_s
        matcher_old = matcher.method_name(old_name).to_s
        define_proxy_call false, self, matcher_new, matcher_old
      end
    end

attribute_alias(name) click to toggle source

Returns the original name for the alias `name`

    # File lib/active_model/attribute_methods.rb, line 223
    def attribute_alias(name)
      attribute_aliases[name.to_s]
    end

attribute_alias?(new_name) click to toggle source

Is `new_name` an alias?

    # File lib/active_model/attribute_methods.rb, line 218
    def attribute_alias?(new_name)
      attribute_aliases.key? new_name.to_s
    end

attribute_method_affix(*affixes) click to toggle source

Declares a method available for all attributes with the given prefix and suffix. Uses `method_missing` and `respond_to?` to rewrite the method.

    #{prefix}#{attr}#{suffix}(*args, &block)

to

    #{prefix}attribute#{suffix}(#{attr}, *args, &block)

An `#{prefix}attribute#{suffix}` instance method must exist and accept at least the `attr` argument.

    class Person
      include ActiveModel::AttributeMethods

      attr_accessor :name
      attribute_method_affix prefix: 'reset_', suffix: '_to_default!'
      define_attribute_methods :name

      private

      def reset_attribute_to_default!(attr)
        send("#{attr}=", 'Default Name')
      end
    end

    person = Person.new
    person.name                         # => 'Gem'
    person.reset_name_to_default!
    person.name                         # => 'Default Name'

    # File lib/active_model/attribute_methods.rb, line 179
    def attribute_method_affix(*affixes)
      self.attribute_method_matchers += affixes.map! { |affix| AttributeMethodMatcher.new prefix: affix[:prefix], suffix: affix[:suffix] }
      undefine_attribute_methods
    end

attribute_method_prefix(*prefixes) click to toggle source

Declares a method available for all attributes with the given prefix. Uses `method_missing` and `respond_to?` to rewrite the method.

    #{prefix}#{attr}(*args, &block)

to

    #{prefix}attribute(#{attr}, *args, &block)

An instance method `#{prefix}attribute` must exist and accept at least the `attr` argument.

    class Person
      include ActiveModel::AttributeMethods

      attr_accessor :name
      attribute_method_prefix 'clear_'
      define_attribute_methods :name

      private

      def clear_attribute(attr)
        send("#{attr}=", nil)
      end
    end

    person = Person.new
    person.name = 'Bob'
    person.name          # => "Bob"
    person.clear_name
    person.name          # => nil

    # File lib/active_model/attribute_methods.rb, line 108
    def attribute_method_prefix(*prefixes)
      self.attribute_method_matchers += prefixes.map! { |prefix| AttributeMethodMatcher.new prefix: prefix }
      undefine_attribute_methods
    end

attribute_method_suffix(*suffixes) click to toggle source

Declares a method available for all attributes with the given suffix. Uses `method_missing` and `respond_to?` to rewrite the method.

    #{attr}#{suffix}(*args, &block)

to

    attribute#{suffix}(#{attr}, *args, &block)

An `attribute#{suffix}` instance method must exist and accept at least the `attr` argument.

    class Person
      include ActiveModel::AttributeMethods

      attr_accessor :name
      attribute_method_suffix '_short?'
      define_attribute_methods :name

      private

      def attribute_short?(attr)
        send(attr).length < 5
      end
    end

    person = Person.new
    person.name = 'Bob'
    person.name          # => "Bob"
    person.name_short?   # => true

    # File lib/active_model/attribute_methods.rb, line 143
    def attribute_method_suffix(*suffixes)
      self.attribute_method_matchers += suffixes.map! { |suffix| AttributeMethodMatcher.new suffix: suffix }
      undefine_attribute_methods
    end

define_attribute_method(attr_name) click to toggle source

Declares an attribute that should be prefixed and suffixed by `ActiveModel::AttributeMethods`.

To use, pass an attribute name (as string or symbol). Be sure to declare `define_attribute_method` after you define any prefix, suffix or affix method, or they will not hook in.

    class Person
      include ActiveModel::AttributeMethods

      attr_accessor :name
      attribute_method_suffix '_short?'

      # Call to define_attribute_method must appear after the
      # attribute_method_prefix, attribute_method_suffix or
      # attribute_method_affix declarations.
      define_attribute_method :name

      private

      def attribute_short?(attr)
        send(attr).length < 5
      end
    end

    person = Person.new
    person.name = 'Bob'
    person.name        # => "Bob"
    person.name_short? # => true

    # File lib/active_model/attribute_methods.rb, line 284
    def define_attribute_method(attr_name)
      attribute_method_matchers.each do |matcher|
        method_name = matcher.method_name(attr_name)

        unless instance_method_already_implemented?(method_name)
          generate_method = "define_method_#{matcher.method_missing_target}"

          if respond_to?(generate_method, true)
            send(generate_method, attr_name.to_s)
          else
            define_proxy_call true, generated_attribute_methods, method_name, matcher.method_missing_target, attr_name.to_s
          end
        end
      end
      attribute_method_matchers_cache.clear
    end

define_attribute_methods(*attr_names) click to toggle source

Declares the attributes that should be prefixed and suffixed by `ActiveModel::AttributeMethods`.

To use, pass attribute names (as strings or symbols). Be sure to declare `define_attribute_methods` after you define any prefix, suffix or affix methods, or they will not hook in.

    class Person
      include ActiveModel::AttributeMethods

      attr_accessor :name, :age, :address
      attribute_method_prefix 'clear_'

      # Call to define_attribute_methods must appear after the
      # attribute_method_prefix, attribute_method_suffix or
      # attribute_method_affix declarations.
      define_attribute_methods :name, :age, :address

      private

      def clear_attribute(attr)
        send("#{attr}=", nil)
      end
    end

    # File lib/active_model/attribute_methods.rb, line 251
    def define_attribute_methods(*attr_names)
      attr_names.flatten.each { |attr_name| define_attribute_method(attr_name) }
    end

undefine_attribute_methods() click to toggle source

Removes all the previously dynamically defined methods from the class.

    class Person
      include ActiveModel::AttributeMethods

      attr_accessor :name
      attribute_method_suffix '_short?'
      define_attribute_method :name

      private

      def attribute_short?(attr)
        send(attr).length < 5
      end
    end

    person = Person.new
    person.name = 'Bob'
    person.name_short? # => true

    Person.undefine_attribute_methods

    person.name_short? # => NoMethodError

    # File lib/active_model/attribute_methods.rb, line 324
    def undefine_attribute_methods
      generated_attribute_methods.module_eval do
        instance_methods.each { |m| undef_method(m) }
      end
      attribute_method_matchers_cache.clear
    end

### Private Instance Methods

attribute_method_matchers_cache() click to toggle source

The methods `method_missing` and `respond_to?` of this module are invoked often in a typical rails, both of which invoke the method `matched_attribute_method`. The latter method iterates through an array doing regular expression matches, which results in a lot of object creations. Most of the time it returns a `nil` match. As the match result is always the same given a `method_name`, this cache is used to alleviate the GC, which ultimately also speeds up the app significantly (in our case our test suite finishes 10% faster with this cache).

    # File lib/active_model/attribute_methods.rb, line 351
    def attribute_method_matchers_cache
      @attribute_method_matchers_cache ||= Concurrent::Map.new(initial_capacity: 4)
    end

attribute_method_matchers_matching(method_name) click to toggle source

    # File lib/active_model/attribute_methods.rb, line 355
    def attribute_method_matchers_matching(method_name)
      attribute_method_matchers_cache.compute_if_absent(method_name) do
        # Must try to match prefixes/suffixes first, or else the matcher with no prefix/suffix
        # will match every time.
        matchers = attribute_method_matchers.partition(&:plain?).reverse.flatten(1)
        matchers.map { |method| method.match(method_name) }.compact
      end
    end

define_proxy_call(include_private, mod, name, send, *extra) click to toggle source

Define a method `name` in `mod` that dispatches to `send` using the given `extra` args. This falls back on `define_method` and `send` if the given names cannot be compiled.

    # File lib/active_model/attribute_methods.rb, line 367
            def define_proxy_call(include_private, mod, name, send, *extra)
              defn = if NAME_COMPILABLE_REGEXP.match?(name)
                "def #{name}(*args)"
              else
                "define_method(:'#{name}') do |*args|"
              end

              extra = (extra.map!(&:inspect) << "*args").join(", ".freeze)

              target = if CALL_COMPILABLE_REGEXP.match?(send)
                "#{"self." unless include_private}#{send}(#{extra})"
              else
                "send(:'#{send}', #{extra})"
              end

              mod.module_eval "            #{defn}
                  #{target}
                end
    ", __FILE__, __LINE__ + 1
            end

instance_method_already_implemented?(method_name) click to toggle source

    # File lib/active_model/attribute_methods.rb, line 338
    def instance_method_already_implemented?(method_name)
      generated_attribute_methods.method_defined?(method_name)
    end