如何使用中间件在mongoose钩子中保存用户

const mongoose = require('mongoose');
const bcrypt = require('bcrypt');

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

// 在保存用户之前执行的逻辑
userSchema.pre('save', async function(next) {
  const user = this;

  // 对密码进行加密
  const salt = await bcrypt.genSalt(10);
  const hashedPassword = await bcrypt.hash(user.password, salt);

  user.password = hashedPassword;
  next();
});

const User = mongoose.model('User', userSchema);

const express = require('express');
const router = express.Router();
const User = require('../models/User');

router.post('/users', async (req, res) => {
  try {
    const { username, password } = req.body;

    // 创建用户
    const user = new User({ username, password });

    // 保存用户
    await user.save();

    res.status(201).json({ message: 'User created successfully' });
  } catch (error) {
    res.status(500).json({ error: 'Failed to create user' });
  }
});

module.exports = router;