# File activemodel/lib/active_model/attribute_methods.rb, line 209
def alias_attribute(new_name, old_name)
  self.attribute_aliases = attribute_aliases.merge(new_name.to_s => old_name.to_s)
  ActiveSupport::CodeGenerator.batch(self, __FILE__, __LINE__) do |code_generator|
    attribute_method_matchers.each do |matcher|
      method_name = matcher.method_name(new_name).to_s
      target_name = matcher.method_name(old_name).to_s
      parameters = matcher.parameters

      mangled_name = target_name
      unless NAME_COMPILABLE_REGEXP.match?(target_name)
        mangled_name = "__temp__#{target_name.unpack1("h*")}"
      end

      code_generator.define_cached_method(method_name, as: mangled_name, namespace: :alias_attribute) do |batch|
        body = if CALL_COMPILABLE_REGEXP.match?(target_name)
          "self.#{target_name}(#{parameters || ''})"
        else
          call_args = [":'#{target_name}'"]
          call_args << parameters if parameters
          "send(#{call_args.join(", ")})"
        end

        modifier = matcher.parameters == FORWARD_PARAMETERS ? "ruby2_keywords " : ""

        batch <<
          "#{modifier}def #{mangled_name}(#{parameters || ''})" <<
          body <<
          "end"
      end
    end
  end
end

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 activemodel/lib/active_model/attribute_methods.rb, line 248
def attribute_alias(name)
  attribute_aliases[name.to_s]
end

Returns the original name for the alias name

# File activemodel/lib/active_model/attribute_methods.rb, line 243
def attribute_alias?(new_name)
  attribute_aliases.key? new_name.to_s
end

Is new_name an alias?

# File activemodel/lib/active_model/attribute_methods.rb, line 180
def attribute_method_affix(*affixes)
  self.attribute_method_matchers += affixes.map! { |affix| AttributeMethodMatcher.new(**affix) }
  undefine_attribute_methods
end

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 activemodel/lib/active_model/attribute_methods.rb, line 109
def attribute_method_prefix(*prefixes, parameters: nil)
  self.attribute_method_matchers += prefixes.map! { |prefix| AttributeMethodMatcher.new(prefix: prefix, parameters: parameters) }
  undefine_attribute_methods
end

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 activemodel/lib/active_model/attribute_methods.rb, line 144
def attribute_method_suffix(*suffixes, parameters: nil)
  self.attribute_method_matchers += suffixes.map! { |suffix| AttributeMethodMatcher.new(suffix: suffix, parameters: parameters) }
  undefine_attribute_methods
end

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 activemodel/lib/active_model/attribute_methods.rb, line 311
def define_attribute_method(attr_name, _owner: generated_attribute_methods)
  ActiveSupport::CodeGenerator.batch(_owner, __FILE__, __LINE__) do |owner|
    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.target}"

        if respond_to?(generate_method, true)
          send(generate_method, attr_name.to_s, owner: owner)
        else
          define_proxy_call(owner, method_name, matcher.target, matcher.parameters, attr_name.to_s, namespace: :active_model)
        end
      end
    end
    attribute_method_matchers_cache.clear
  end
end

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 activemodel/lib/active_model/attribute_methods.rb, line 276
def define_attribute_methods(*attr_names)
  ActiveSupport::CodeGenerator.batch(generated_attribute_methods, __FILE__, __LINE__) do |owner|
    attr_names.flatten.each { |attr_name| define_attribute_method(attr_name, _owner: owner) }
  end
end

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 activemodel/lib/active_model/attribute_methods.rb, line 353
def undefine_attribute_methods
  generated_attribute_methods.module_eval do
    undef_method(*instance_methods)
  end
  attribute_method_matchers_cache.clear
end

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