使用Knex向MySQL插入数据失败：Cannot read properties of undefined报错排查

错误根源 #

你的/signUp路由处理函数参数写错了——把Express路由的第三个参数（本该是next）写成了db，这直接覆盖了全局定义的Knex实例，导致函数内部的db变成undefined，调用db('users').insert()时就会抛出Cannot read properties of undefined (reading 'insert')错误。

修复后的完整代码 #

只需删除路由参数里多余的db，直接使用全局的Knex实例即可：

const db= knex ({
  client: 'mysql2',
  connection: {
    host: '127.0.0.1',
    port: 3306,
    user: 'root',
    password: '',
    database: 'transaction_app'
  }
});

app.get('/', (req, res) => {
  res.send('App is running')
});

// 移除参数中的db
app.post('/signUp', (req, res) => {
  const {name, email, mobile, password}=req.body;
  const hash=bcrypt.hashSync(password, 10);

  db('users')
  .insert({
    name: name,
    email: email,
    mobile: mobile,
    password: hash
  })
  .then(data=>{
    res.send(data);
  })
  .catch(err=>{
    res.send(err);
  })
});

app.get('/fetch',(req,res)=>{
  db.select('*').from('users')
  .then(data=>{
    res.send(data);
  })
  .catch(err=>{
    res.send(err);
  })
})

app.listen(3000, () =>{
  console.log('Server started on port 3000');
});

额外优化建议 #

1. 确保已添加express.json()中间件，否则Postman发送的JSON参数无法被解析，req.body会是undefined：

app.use(express.json());

2. 错误处理可以更规范，返回JSON格式的错误信息：

.catch(err=>{
  res.status(500).json({error: err.message});
})

原控制台报错信息 #

Server started on port 3000
users
TypeError: Cannot read properties of undefined (reading 'insert')
    at D:\Documents\Atoa Assignment\server.js:35:3
    at Layer.handle [as handle_request] (D:\Documents\Atoa Assignment\node_modules\express\lib\router\layer.js:95:5)
    at next (D:\Documents\Atoa Assignment\node_modules\express\lib\router\route.js:144:13)
    at Route.dispatch (D:\Documents\Atoa Assignment\node_modules\express\lib\router\route.js:114:3)
    at Layer.handle [as handle_request] (D:\Documents\Atoa Assignment\node_modules\express\lib\router\layer.js:95:5)
    at D:\Documents\Atoa Assignment\node_modules\express\lib\router\index.js:284:15
    at Function.process_params (D:\Documents\Atoa Assignment\node_modules\express\lib\router\index.js:346:12)
    at next (D:\Documents\Atoa Assignment\node_modules\express\lib\router\index.js:280:10)
    at cors (D:\Documents\Atoa Assignment\node_modules\cors\lib\index.js:188:7)    at D:\Documents\Atoa Assignment\node_modules\cors\lib\index.js:224:17

Postman请求截图 #

内容的提问来源于stack exchange，提问作者NevinTroy