Extend the fields of a Mongoid document from a .yml file

dynamic_document.rb

module ExtendFields
  require "yaml"

  private
    def extend_fields
      dynamic_fields.each { |name, type| self.class.field name, type: type }
    end

    def dynamic_fields
      YAML.load_file( File.join( Rails.root, 'config', 'class_fields', "#{self.class.name.underscore}.yml" ) ) rescue {}
    end
end

#And then include this module in the class you want to extend
class DynamicDocument
  include ExtendFields
  after_initialize :extend_fields
end