gistfile1.rb

class User < ActiveRecord::Base
  ROLES = %w[admin manager client]

  validates :role, inclusion: {in: ROLES}

  def role
    ActiveSupport::StringInquirer.new(self[:role].to_s)
  end
end

user = User.create!(role: "manager")
user.role.admin? # => false
user.role.manager? # => true