Override a Mongoid model's setters and getters

Is there a way to override a setter or getter for a model in Mongoid? Something like:

class Project
  include Mongoid::Document
  field :name, :type => String
  field :num_users, type: Integer, default: 0
  key :name
  has_and_belongs_to_many :users, class_name: "User", inverse_of: :projects

  # This will not work
  def name=(projectname)
    @name = projectname.capitalize
  end
end

where the name method can be overwritten without using virtual fields?