module ActiveRecord # Declare an enum attribute where the values map to integers in the database, but can be queried by name. Example: # # class Conversation < ActiveRecord::Base # enum status: [ :active, :archived ] # end # # # conversation.update! status: 0 # conversation.active! # conversation.active? # => true # conversation.status # => "active" # # # conversation.update! status: 1 # conversation.archived! # conversation.archived? # => true # conversation.status # => "archived" # # # conversation.update! status: 1 # conversation.status = "archived" # # You can set the default value from the database declaration, like: # # create_table :conversations do |t| # t.column :status, :integer, default: 0 # end # # Good practice is to let the first declared status be the default. # # Finally, it's also possible to explicitly map the relation between attribute and # database integer with a +Hash+: # # class Conversation < ActiveRecord::Base # enum status: { active: 0, archived: 1 } # end # # Note that when an +Array+ is used, the implicit mapping from the values to database # integers is derived from the order the values appear in the array. In the example, # :active is mapped to +0+ as it's the first element, and :archived # is mapped to +1+. In general, the +i+-th element is mapped to i-1 in the # database. # # Therefore, once a value is added to the enum array, its position in the array must # be maintained, and new values should only be added to the end of the array. To # remove unused values, the explicit +Hash+ syntax should be used. # # In rare circumstances you might need to access the mapping directly. # The mappings are exposed through a constant with the attributes name: # # Conversation::STATUS # => { "active" => 0, "archived" => 1 } # # Use that constant when you need to know the ordinal value of an enum: # # Conversation.where("status <> ?", Conversation::STATUS[:archived]) module Enum def enum(definitions) klass = self definitions.each do |name, values| # STATUS = { } enum_values = _enum_methods_module.const_set name.to_s.upcase, ActiveSupport::HashWithIndifferentAccess.new name = name.to_sym _enum_methods_module.module_eval do # def status=(value) self[:status] = STATUS[value] end define_method("#{name}=") { |value| unless enum_values.has_key?(value) raise ArgumentError, "'#{value}' is not a valid #{name}" end self[name] = enum_values[value] } # def status() STATUS.key self[:status] end define_method(name) { enum_values.key self[name] } pairs = values.respond_to?(:each_pair) ? values.each_pair : values.each_with_index pairs.each do |value, i| enum_values[value] = i # scope :active, -> { where status: 0 } klass.scope value, -> { klass.where name => i } # def active?() status == 0 end define_method("#{value}?") { self[name] == i } # def active!() update! status: :active end define_method("#{value}!") { update! name => value } end end end end private def _enum_methods_module @_enum_methods_module ||= begin mod = Module.new include mod mod end end end end