How do i specify and validate an enum in rails?

Question

I currently have a model Attend that will have a status column, and this status column will only have a few values for it. STATUS_OPTIONS = {:yes, :no, :maybe}

1)

Answer 1

Now that Rails 4.1 includes enums you can do the following:

class Attend < ActiveRecord::Base
    enum size: [:yes, :no, :maybe]
    # also can use the %i() syntax for an array of symbols:
    # %i(yes no maybe)
    validates :size, inclusion: { in: sizes.keys }
end

Which then provides you with a scope (ie: Attend.yes, Attend.no, Attend.maybe for each a checker method to see if certain status is set (ie: #yes?, #no?, #maybe?), along with attribute setter methods (ie: #yes!, #no!, #maybe!).

Rails Docs on enums

Answer 2

To define dynamic behavior you can use in: :method_name notation:

class Attend < ActiveRecord::Base
  enum status: [:yes, :no, :maybe]
  validates :status, inclusion: {in: :allowed_statuses}

  private

  # restricts status to be changed from :no to :yes
  def allowed_statuses
    min_status = Attend.statuses[status_was]
    Attend.statuses.select { |_, v| v >= min_status }.keys
  end
end

Answer 3

For enums in ActiveModels you can use this gem Enumerize

Answer 4

After some looking, I could not find a one-liner in model to help it happen. By now, Rails provides Enums, but not a comprehensive way to validate invalid values.

So, I opted for a composite solution: To add a validation in the controller, before setting the strong_params, and then by checking against the model.

So, in the model, I will create an attribute and a custom validation:

attend.rb

enum :status => { your set of values }
attr_accessor :invalid_status

validate :valid_status
#...
private
    def valid_status
        if self.invalid_status == true
            errors.add(:status, "is not valid")
        end
    end

Also, I will do a check against the parameters for invalid input and send the result (if necessary) to the model, so an error will be added to the object, thus making it invalid

attends_controller.rb

private
    def attend_params
        #modify strong_params to include the additional check
        if params[:attend][:status].in?(Attend.statuses.keys << nil) # to also allow nil input
            # Leave this as it was before the check
            params.require(:attend).permit(....) 
        else
            params[:attend][:invalid_status] = true
            # remove the 'status' attribute to avoid the exception and
            # inject the attribute to the params to force invalid instance
            params.require(:attend).permit(...., :invalid_status)
       end
    end

Answer 5

Create a globally accessible array of the options you want, then validate the value of your status column:

class Attend < ActiveRecord::Base

  STATUS_OPTIONS = %w(yes no maybe)

  validates :status, :inclusion => {:in => STATUS_OPTIONS}

end

You could then access the possible statuses via Attend::STATUS_OPTIONS

Answer 6

You could use a string column for the status and then the :inclusion option for validates to make sure you only get what you're expecting:

class Attend < ActiveRecord::Base
    validates :size, :inclusion => { :in => %w{yes no maybe} }
    #...
end