问题

我在使用Express JS模型返回结果时遇到了问题。我认为我的问题在于对回调和JS类的理解不够。我似乎无法让它工作。

我有以下代码。

从server.js中，我有这个路由：

app.get('/api/v1/loralocations/:id', LoraLocation.getOne);

这调用下面的控制器动作：

getOne(req, res) {
  const lora_location = LoraLocationModel.findOne(req.params.id);
  if (!lora_location) {
    return res.status(404).send({'message': 'LoraLocation not found'});
  }
  return res.status(200).send(lora_location);
},

模型：

var pool = require('./mysqlDb.js');
import moment from 'moment';

class LoraLocation {  
  /**
   * class constructor
   * @param {object} data
   */
  constructor() {
  
  }

  findOne(id) {
    var sql = ('SELECT test FROM Test WHERE id = ?');
    pool.query(sql, [id], function (err, results, fields) {
      if (err) return err;  
      console.log(results); //works
      return results; //nope
    });
  }
}

控制台输出结果，但没有返回到控制器。我已经查看了许多帖子，但似乎找不到解决方法。我认为控制器中可能也需要一个回调？

这是否是一个简单API项目的标准模式？

谢谢

英文:

I am having an issue returning results from a Express JS model. I think my problem is a lack of understanding of callbacks and JS Classes. I just can't seem to make it work.

I have the following code.

From the server.js I have this route:

app.get(&#39;/api/v1/loralocations/:id&#39;, LoraLocation.getOne);

Which calls the Controller action below

getOne(req, res) {
  const lora_location = LoraLocationModel.findOne(req.params.id);
  if (!lora_location) {
    return res.status(404).send({&#39;message&#39;: &#39;LoraLocation not found&#39;});
 }
 return res.status(200).send(lora_location);
},
.
.
.

Model

var pool = require(&#39;./mysqlDb.js&#39;);
import moment from &#39;moment&#39;;

class LoraLocation {  
  /**
   * class constructor
   * @param {object} data
   */
  constructor() {
  
  }
    
findOne(id) {
    var sql = (&#39;SELECT test FROM Test WHERE id = ?&#39;);
    pool.query(sql, [id], function (err, results, fields) {
      if (err) return err;  
      console.log(results); //works
      return results; //nope
    });
  }

The console.log returns the results, but nothing is returned to the controller. I have gone through a number of posts but can't seem to find a solution. I think maybe I need a callback in the controller also?

Would this be a fairly standard pattern for a simple API project?

Thanks

答案1

得分: 0

你正在不正确地使用回调。要么你可以使用async/await，这是一个不错的选择，要么如果你想坚持使用回调，那么你需要返回回调函数。

控制器

const lora_location = LoraLocationModel.findOne(req.params.id, function (err, data) => {
});

在模型中应该是这样的

findOne(id, cb) {
    var sql = ('SELECT test FROM Test WHERE id = ?');
    pool.query(sql, [id], function (err, results, fields) {
      if (err) cb(err, []);  
      console.log(results); //works
      cb(null, results);
    });
  }

你可以在这个链接中获取有关回调的更多详细信息
https://medium.com/better-programming/callbacks-in-node-js-how-why-when-ac293f0403ca

英文:

You are using callback incorrectly.
either you can use async/await which is a good option or if you want to stick with callbacks then you need to return callback function.

controllers

const lora_location = LoraLocationModel.findOne(req.params.id, function (err, data) =&gt; {
});

in the model it should be

findOne(id, cb) {
    var sql = (&#39;SELECT test FROM Test WHERE id = ?&#39;);
    pool.query(sql, [id], function (err, results, fields) {
      if (err) cb(err, []);  
      console.log(results); //works
      cb(null, results);
    });
  }

you can get more details for callbacks in this link
https://medium.com/better-programming/callbacks-in-node-js-how-why-when-ac293f0403ca

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