def init
        @sender = User.new(@sender) if @sender.is_a?(Hash)
        @recipient = User.new(@recipient) if @recipient.is_a?(Hash)
        @created_at = Time.parse(@created_at) if @created_at.is_a?(String)
      end
def init
        @sender = User.new(@sender) if @sender.is_a?(Hash)
        @recipient = User.new(@recipient) if @recipient.is_a?(Hash)
        @created_at = Time.parse(@created_at) if @created_at.is_a?(String)
      end
Constructor callback