如何等待續集執行findOne

Question

我有一個使用Sequelize.js的路線

app.get('/api/users/:username', (req, res) => {
  const foundUser = getUserByUsername(req.params.username);
  console.log(`foundUser = ${foundUser}`);
  return res.send(foundUser);
});

getUserByUsername函數如下

const getUserByUsername = username => {
  Viewer.findOne({
    where: {username}
  }).then(response => {
    console.log(response.dataValues);//the object with the data I need
    return response.dataValues;
  });
};

我希望在我的路由中將對象保存在我的const foundUser中，但是似乎我需要等到findOne被執行，因為在我的控制台中，我可以看到foundUser的日志（當時是未定義的）在執行之前函數getUserByUsername

foundUser = undefined
Executing (default): SELECT `id`, `username`, `instakluiten`, `role`, `createdAt`, `updatedAt` FROM `viewers` AS `viewer` WHERE `viewer`.`username` = 'instak' LIMIT 1;
{ id: 19,
  username: 'instak',
  instakluiten: 18550,
  role: 'moderators',
  createdAt: 2016-10-02T16:27:44.000Z,
  updatedAt: 2016-10-09T10:17:40.000Z }

如何確定我的foundUser將使用已找到用戶的數據進行更新？

Answer 1

您必須返回 Sequelize創建的承諾，然后等待其解決。 因此， getUserByUsername變為：

const getUserByUsername = username => {
  return Viewer.findOne({
    where: {username}
  }).then(response => {
    console.log(response.dataValues);//the object with the data I need
    return response.dataValues;
  });
};

並在路線中：

app.get('/api/users/:username', (req, res) => {
  getUserByUsername(req.params.username).then(foundUser => {
    res.send(foundUser);
  });
});

這是因為您需要遵守承諾鏈。 如果您忘記返回它，即使最終解決了Promise，函數也會返回undefined end，它所解析的值永遠不會回到鏈中。

Answer 2

app.get('/api/users/:username', (req, res) => {
getUserByUsername(req.params.username, function(err, result){
const foundUser = result;
console.log(`foundUser = ${foundUser}`);
 res.send(foundUser); 
});

});



const getUserByUsername = function(username, callback) {
Viewer.findOne({
where: {username}
}).then(response => {
console.log(response.dataValues);//the object with the data I need
return callback(null, response.dataValues);
});
};

Answer 3

您可以通過promise或callback避免它

app.get('/api/users/:username', (req, res) => {
  getUserByUsername(req.params.username, function(err, foundUser) {
    if (!err) {
      console.log(`foundUser = ${foundUser}`);
      return res.send(foundUser);
    } else {
      res.send(err)
    }
  });
});



const getUserByUsername = (username, callback) => {
  Viewer.findOne({
    where: {
      username
    }
  }).then(response => {
    console.log(response.dataValues); //the object with the data I need
    return callback(null, response.dataValues);
  });
};