Mongoose schema.pre（'；save'；）不会触发

嗨，我计划在pre方法触发后打印出

pre

，但它不起作用

import mongoose from'mongoose'
mongoose.connect('mongodb://localhost/test', { useNewUrlParser: true, useUnifiedTopology: true });
const db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function() {
  console.log('connected')
});

// test for pre hooks
const toySchema = mongoose.Schema({ name: String, created: Date });
const Toy = mongoose.model('Toy', toySchema)

toySchema.pre('save', function(next) {
  if (!this.created) this.created = new Date;
  console.log('pre');
  next(new Error('something went wrong'));
});

const firstoy = new Toy({ name: 'tank' })
firstoy.save(function (err, firstoy) {
  if (err) return console.error(err);
});

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找到书面答案：在编译模型之前定义中间件