如何定义一个将Promise返回Express Express函数的函数？

I have a business leve database module called "db_location" which uses the node-fetch module to get some data from a remote server via REST API.

我有一个名为“db_location”的业务级别数据库模块，它使用node-fetch模块通过REST API从远程服务器获取一些数据。

**db_location.js** DB LOGIC

const p_conf = require('../parse_config');

const db_location = {
    getLocations: function() {

        fetch(`${p_conf.SERVER_URL}/parse` + '/classes/GCUR_LOCATION', { method: 'GET', headers: {
            'X-Parse-Application-Id': 'APPLICATION_ID',
            'X-Parse-REST-API-Key': 'restAPIKey'
        }})
        .then( res1 => {
            //console.log("res1.json(): " + res1.json());
            return res1;
        })
        .catch((error) => {
            console.log(error);
            return Promise.reject(new Error(error));
        })
    }

};

module.exports = db_location

I would need to call this function within a Route function so as to separate database processing from controller.

我需要在Route函数中调用此函数，以便将数据库处理与控制器分开。

**locations.js** ROUTE

var path = require('path');
var express = require('express');
var fetch = require('node-fetch');
var router = express.Router();

const db_location = require('../db/db_location');

/* GET route root page. */
router.get('/', function(req, res, next) {

  db_location.getLocations()
  .then(res1 => res1.json())
  .then(json => res.send(json["results"]))
  .catch((err) => {
    console.log(err);
    return next(err);
  })
});

When I ran http://localhost:3000/locations, I received the following error.

当我运行http：// localhost：3000 / locations时，我收到以下错误。

Cannot read property 'then' of undefined

TypeError: Cannot read property 'then' of undefined

It seems the Promise was empty or something wrong down the Promise chain going from one response object to another? What is a best practise for solving this kind of scenario?

似乎Promise是空的，或者Promise链从一个响应对象转到另一个响应对象时出现了什么问题？解决这种情况的最佳做法是什么？

EDIT 1

编辑1

If I changed the getLocations to return res1.json() (which I think is a non-empty Promise according to the node-fetch documentation):

如果我更改了getLocations以返回res1.json（）（根据node-fetch文档，我认为它是非空的Promise）：

fetch(`${p_conf.SERVER_URL}/parse` + '/classes/GCUR_LOCATION', { method: 'GET', headers: {
        'X-Parse-Application-Id': 'APPLICATION_ID',
        'X-Parse-REST-API-Key': 'restAPIKey'
    }})
    .then(  res1 => {
       return res1.json();     // Not empty as it can be logged to `Promise Object`
    })
    .catch((error) => {
        console.log(error);
        return Promise.reject(new Error(error));
    })

And the route code was changed to :

并且路线代码更改为：

db_location.getLocations()
  .then(json => res.send(json["results"]))
  .catch((err) => {
    console.log(err);
    return next(err);
  })

The exactly same error was thrown.

抛出了完全相同的错误。

2 个解决方案

#1

You need getLocations to return a Promise. At the moment, it's running a fetch, but that fetch isn't connected to anything else, and getLocations is returning undefined (and of course you can't call .then on uundefined)

你需要getLocations来返回一个Promise。目前，它正在运行一个fetch，但是fetch没有连接到任何其他东西，并且getLocations返回undefined（当然你不能在uundefined上调用.then）

Instead, change to:

相反，改为：

const db_location = {
  getLocations: function() {
    return fetch( ...

Also, since you're not doing anything special in the getLocations catch block, you might consider omitting it entirely and let the caller handle it.

此外，由于您没有在getLocations catch块中执行任何特殊操作，因此您可以考虑完全省略它并让调用者处理它。

#2

Your function doesn't return anything.

你的功能没有返回任何东西。

If you want to use a promise, you need return it.

如果您想使用承诺，则需要退货。

#1