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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.status = 1
conversation.status = "archived"

conversation.status = nil
conversation.status.nil? # => true
conversation.status      # => nil

Scopes based on the allowed values of the enum field will be provided as well. With the above example:

Conversation.active
Conversation.archived

Of course, you can also query them directly if the scopes don't fit your needs:

Conversation.where(status: [:active, :archived])
Conversation.where.not(status: :active)

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 class method with the pluralized attribute name, which return the mapping in a HashWithIndifferentAccess:

Conversation.statuses[:active]    # => 0
Conversation.statuses["archived"] # => 1

Use that class method when you need to know the ordinal value of an enum. For example, you can use that when manually building SQL strings:

Conversation.where("status <> ?", Conversation.statuses[:archived])

You can use the :_prefix or :_suffix options when you need to define multiple enums with same values. If the passed value is true, the methods are prefixed/suffixed with the name of the enum. It is also possible to supply a custom value:

class Conversation < ActiveRecord::Base
  enum status: [:active, :archived], _suffix: true
  enum comments_status: [:active, :inactive], _prefix: :comments
end

With the above example, the bang and predicate methods along with the associated scopes are now prefixed and/or suffixed accordingly:

conversation.active_status!
conversation.archived_status? # => false

conversation.comments_inactive!
conversation.comments_active? # => false
Namespace
Methods
E
Constants
ENUM_CONFLICT_MESSAGE = \ "You tried to define an enum named \"%{enum}\" on the model \"%{klass}\", but " \ "this will generate a %{type} method \"%{method}\", which is already defined " \ "by %{source}."
 
Instance Public methods
enum(definitions)
# File activerecord/lib/active_record/enum.rb, line 139
def enum(definitions)
  klass = self
  enum_prefix = definitions.delete(:_prefix)
  enum_suffix = definitions.delete(:_suffix)
  definitions.each do |name, values|
    # statuses = { }
    enum_values = ActiveSupport::HashWithIndifferentAccess.new
    name        = name.to_sym

    # def self.statuses statuses end
    detect_enum_conflict!(name, name.to_s.pluralize, true)
    klass.singleton_class.send(:define_method, name.to_s.pluralize) { enum_values }

    detect_enum_conflict!(name, name)
    detect_enum_conflict!(name, "#{name}=")

    attribute name, EnumType.new(name, enum_values)

    _enum_methods_module.module_eval do
      pairs = values.respond_to?(:each_pair) ? values.each_pair : values.each_with_index
      pairs.each do |value, i|
        if enum_prefix == true
          prefix = "#{name}_"
        elsif enum_prefix
          prefix = "#{enum_prefix}_"
        end
        if enum_suffix == true
          suffix = "_#{name}"
        elsif enum_suffix
          suffix = "_#{enum_suffix}"
        end

        value_method_name = "#{prefix}#{value}#{suffix}"
        enum_values[value] = i

        # def active?() status == 0 end
        klass.send(:detect_enum_conflict!, name, "#{value_method_name}?")
        define_method("#{value_method_name}?") { self[name] == value.to_s }

        # def active!() update! status: :active end
        klass.send(:detect_enum_conflict!, name, "#{value_method_name}!")
        define_method("#{value_method_name}!") { update! name => value }

        # scope :active, -> { where status: 0 }
        klass.send(:detect_enum_conflict!, name, value_method_name, true)
        klass.scope value_method_name, -> { klass.where name => value }
      end
    end
    defined_enums[name.to_s] = enum_values
  end
end