问Mongoose预更新钩子工作，但更改不会反映在数据库中

EN

const Contact = new mongoose.Schema({
  firstName: { type: String, required: true },
  middleName: { type: String, required: false },
  lastName: { type: String, required: true },
  fullName: { type: String, required: false },
});

// When a Contact is created, we populate the `fullName` field using a pre-save
// hook, which is working as expected:

Contact.pre('save', function (next) {
  const contact = this;
  contact.fullName = `${contact.firstName || ''} ${contact.lastName || ''}`;
  
  return next();
});

// on update, we want to update the fullName field as well. This is broken:

Contact.pre(\(updateOne|update)\, function (next) {
  const contact = this;
  const update = contact._update['$set'];

  const newFullName = `${update['firstName'] || ''} ${update['lastName'] || ''}`;
  console.log(newFullName);

  contact.fullName = newFullName;

  console.log(contact.fullName);  // i can see the correctly updated value here!

  if (update['middleName']) contact.middleName = update['middleName'];

  console.log(contact.middleName);  // i can also see this one!
  
  return next();
});

module.exports.updateContact = (req, res, next) => {
  const { contact } = req.body;

  Contact.updateOne({ _id: contactId }, { $set: { ...contact } }, (err, result) => {
    if (err) return next(err);

    return next(result);
  });
};