module ActiveRecord class Attribute # :nodoc: class << self def from_database(name, value, type) FromDatabase.new(name, value, type) end def from_user(name, value, type) FromUser.new(name, value, type) end def null(name) Null.new(name) end def uninitialized(name, type) Uninitialized.new(name, type) end end attr_reader :name, :value_before_type_cast, :type # This method should not be called directly. # Use #from_database or #from_user def initialize(name, value_before_type_cast, type) @name = name @value_before_type_cast = value_before_type_cast @type = type end def value # `defined?` is cheaper than `||=` when we get back falsy values @value = type_cast(value_before_type_cast) unless defined?(@value) @value end def value_for_database type.type_cast_for_database(value) end def changed_from?(old_value) type.changed?(old_value, value, value_before_type_cast) end def changed_in_place_from?(old_value) type.changed_in_place?(old_value, value) end def with_value_from_user(value) self.class.from_user(name, value, type) end def with_value_from_database(value) self.class.from_database(name, value, type) end def type_cast raise NotImplementedError end def initialized? true end protected def initialize_dup(other) if defined?(@value) && @value.duplicable? @value = @value.dup end end class FromDatabase < Attribute # :nodoc: def type_cast(value) type.type_cast_from_database(value) end end class FromUser < Attribute # :nodoc: def type_cast(value) type.type_cast_from_user(value) end end class Null < Attribute # :nodoc: def initialize(name) super(name, nil, Type::Value.new) end def value nil end def with_value_from_database(value) raise ActiveModel::MissingAttributeError, "can't write unknown attribute `#{name}`" end alias_method :with_value_from_user, :with_value_from_database end class Uninitialized < Attribute # :nodoc: def initialize(name, type) super(name, nil, type) end def value if block_given? yield name end end def value_for_database end def initialized? false end end private_constant :FromDatabase, :FromUser, :Null, :Uninitialized end end