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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,
# <tt>:active</tt> is mapped to +0+ as it's the first element, and <tt>:archived</tt>
# is mapped to +1+. In general, the +i+-th element is mapped to <tt>i-1</tt> 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
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