code: function (query, update, fship) {
      var options = { new: false };
  
      return function (done) {
        this.findOneAndUpdate(query, update, options, function (err, res) {
          done(err, fship);
        });
      }
    }
docs: The work function which pushes or updates embedded friend objects
  for two documents, returns a function
  
  @api private