Question

我正在制作类似社交媒体的网站，用户可以互相关注。在我的一条路线中，我想遍历当前用户，紧跟着是ID数组的数组，找到这些用户的帖子并将其添加到一个大数组中，然后按日期对帖子进行排序。问题是在将帖子添加到客户端之前，该数组已发送到客户端。不知道我是否需要某种异步功能或什么。

我获得帖子的路线

const express = require('express')
const user = require("../models/user')
const router = express.Router()

router.get("/api/:username/following/posts", (req, res) => {
    let following = [...req.user.following, req.user._id]
    let posts = [], i;
    for(i = 0; i < following.length; i++){
        User.findById(following[i]).populate("posts")
            .then(user => {
                for(let b = 0; b < user.posts.length; b++){
                    posts.push(user.posts[b])
                }
            })
            .catch(err => {
                console.log(err)
            })
    }
    console.log(posts) // returns []
    res.json(posts) 
})

Answer 1

使用异步/等待

router.get("/api/:username/following/posts", async (req, res) => {
    const following = [...req.user.following, req.user._id]
    const posts = [];
    for(let f of following){
        const user = await User.findById(f).populate("posts");
        posts.push(...user.posts);
    }
    console.log(posts)
    res.json(posts) 
})

仅使用承诺

router.get("/api/:username/following/posts", (req, res) => {
    const following = [...req.user.following, req.user._id];
    Promise.all(following.map(f => User.findBy(f).populate("posts")))
    .then(users => {
        const posts = users.map(({posts}) => posts).flat();
        console.log(posts);
        res.json(posts);
    });
})

主要区别在于，仅Promise的代码将并行调用User.findBy，而async / await将依次调用它们（不用担心，顺序也保持在promise版本中）< / p>

如果并行调用findBy时出现问题，而您仍然不想使用async / await，则可以这样做：

router.get("/api/:username/following/posts", (req, res) => {
    const following = [...req.user.following, req.user._id];
    Promise.all(following.reduce((p, f) => p.then(results => User.findBy(f).populate("posts").then(user => [...results, user])), Promise.resolve([])))
    .then(users => {
        const posts = users.map(({posts}) => posts).flat();
        console.log(posts);
        res.json(posts);
    });
})

Answer 2

您可以使用async / await，也可以将res.json调用移至.then

在将项目添加到诺言中的数组时遇到问题

2 个答案: