如何使Mongoose在模式中未列出字段时不保存

const userSchema = new mongoose.Schema({
  username: String,
  password: String
}, { strict: false });

userSchema.pre('save', function (next) {
  const doc = this;
  Object.keys(doc._doc).forEach((key) => {
    if (!doc.schema.obj.hasOwnProperty(key)) {
      delete doc._doc[key];
    }
  });
  next();
});

const user = new User({
  username: 'example',
  password: 'password',
  age: 25
});

const userObject = user.toObject({ strict: false });