Question

在我的用户架构中，我有一个名为favorites的属性，它存储来自另一个存储引号的数据库的对象ID数组。我想在favorites属性中执行for循环，循环遍历每个id，根据来自其他数据库的id查找引用，将整个引用存储到新数组，然后将所有引用对象添加到array，将包含该数组的变量显示到ejs视图。这是我尝试过的代码：

router.get('/profile', authenticationMiddleware(), (req, res, next) => {
    // console.log("After AuthenticationMiddleware of /profile load: The user username is: ", req.user.id)

    let quoteIdFavorites = req.user.favorites
    console.log("Started off by storing the ids of your favorite quotes to a variable: ", quoteIdFavorites)

    let listOfQuotes = []
    let getUserFavorites = new Promise((resolve, reject) => {
        for (let i = 0; i < quoteIdFavorites.length; i++) {
            Quote.findById({ _id: quoteIdFavorites[i] }, (err, result) => {
                if (err) {
                    console.log("Database Error: ", err.message)
                } else {
                    listOfQuotes.push(result)
                    console.log("Quote added. Iteration " + [i] + ": ", result)
                }
            })
        }
        console.log("Post for loop, here are your listOfQuotes: ", listOfQuotes)
        resolve()
    }).then(() => {
        console.log("Promised resolved, now page should begin loading.")
        console.log("And finally, here is what the listOfQuotes variable has in it: ", listOfQuotes)
        res.render('profile', { user: req.user.username, favorites: listOfQuotes })
    })
})

由于for循环不是一个promise，我试图将它转换为一个，然后一旦整个循环结束，我解析了promise，然后在.then（）方法中，使用listOfQuotes渲染/ profile页面包含所需结果的变量。但是，在将所有结果存储到数组之前，.then（）方法中的代码仍然首先运行。以下是控制台中输出的顺序：

// Step 1:
Started off by storing the ids of your favorite quotes to a variable:  ["59f8defdfc62ebaba24ad627","59f8ddf69ad7b6ab6be6629e"]

// Step 2:
Post for loop, here are your listOfQuotes:  []

// Step 3:
Promised resolved, now page should begin loading.

// Step 4: empty?
And finally, here is what the listOfQuotes variable has in it:  []

// Step 5: load page
GET /profile 200 48.937 ms - 1905

// Step 6: why are the quotes just now being added to the array? the page has already loaded!
Quote added. Iteration 0:  { _id: 59f8defdfc62ebaba24ad627,
  updatedAt: 2017-10-31T20:37:17.279Z,
  createdAt: 2017-10-31T20:37:17.279Z,
  quote: 'how bout now',
  author: 'well',
  __v: 0 }
Quote added. Iteration 1:  { _id: 59f8ddf69ad7b6ab6be6629e,
  updatedAt: 2017-10-31T20:32:54.290Z,
  createdAt: 2017-10-31T20:32:54.290Z,
  quote: 'still work please',
  author: 'thanks',
  __v: 0 }

// Step 7: load in styles
GET /stylesheets/profile.css 200 37.570 ms - 5014
GET /javascripts/main.js 200 11.248 ms - 5800

非常感谢任何帮助！

如何在for循环中执行异步数据库查询？

0 个答案: