Question

我最近被介绍给Promises。我需要将异步操作转换为Promise的帮助。这是代码：


var data = [
        {
            name: "Brandt",
            image: "img.jpg",
            description: "Lorem ipsum"
        },
        {
            name: "Paul",
            image: "img2.jpg",
            description: "ipsum"
        },
        {
            name: "Jim",
            image: "img3.jpg",
            description: "Lorem"
        },
    ];

function seedDB(){
    // remove all campgrounds
    Campground.remove({}, function(err){
        if(err){
            console.log;
        } else {
            console.log("campgrounds removed!");
        }
        // remove all comments
        Comment.remove({}, function(err){
            if (err) {
                console.log(err);
            }
            else {
                console.log("comments removed");
            }
            // add a few campgrounds
            data.forEach(function(seed){
                Campground.create(seed, function(err, campground){
                    if (err){
                        console.log(err);
                    } else {
                        console.log("added a campground");
                        // add a few comments
                        Comment.create({
                            text: "lorem ipsum.",
                            author: "Homer"
                        }, function(err, comment){
                            if (err){
                                console.log(err);
                            }
                            else {
                                campground.comments.push(comment);
                                campground.save();
                                console.log("created new comment");
                            }
                        });
                    }
                });
            });
        });
    });
}

这是我尝试过的：

var seedDB = promisify(Campground.remove);

seedDB({})
.then(() => promisify(Comment.remove({}))
)
.then(() =>
       data.forEach(function(seed){
        Campground.create(seed, function(err, campground){
            if (err){
                console.log(err);
            } else {
                console.log("added a campground");
                // add a few comments
                Comment.create({
                    text: "lorem ipsum.",
                    author: "Homer"
                }, function(err, comment){
                    if (err){
                        console.log(err);
                    }
                    else {
                        campground.comments.push(comment);
                        campground.save();
                        console.log("created new comment");
                    }
                })
            }
        })
    })
)
.catch((err)=>console.log(err))

我正在使用MongoDB和Express。我的尝试引发以下情况：

TypeError: Cannot read property 'Query' of undefined
    at remove (/home/ubuntu/workspace/yelpcamp/v6/node_modules/mongoose/lib/model.js:1697:23)
    at remove (internal/util.js:230:26)
    at Object.<anonymous> (/home/ubuntu/workspace/yelpcamp/v6/seeds.js:77:1)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)
    at Module.require (module.js:596:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (/home/ubuntu/workspace/yelpcamp/v6/index.js:13:14)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)

我知道Promise.all(arr)接受包含一堆异步操作的数组。我可以有这样一个数组，但是对于forEach回调我该怎么办？这些是我的进口商品：

const { promisify } = require("util")
const Promise = require("bluebird")

Answer 1

我已经在朋友的帮助下制定了解决方案。如果有人遇到类似问题，我会发布。在这里：

async function seedDB(){
    try{
        await Campground.remove({});
        console.log("campgrounds removed!");
        await Comment.remove({});
        console.log("comments removed")
        await User.remove({});
        console.log("users removed");
        let user = await User.create({username: 'Stacy', password: 'password'});
        for(let d of data){
            let campground = await Campground.create(d);
            console.log("added campground");
            let comment = await Comment.create({text: "hello", author:user._id});  // this is required because the Comment schema ({text: String, author: ref -> User}) stores a reference to User.
            campground.comments.push(comment);
            await campground.save();
            console.log("comments saved");
        }
    } catch(err){
        console.log(err);
    }
}

无法将回调地狱变成承诺

1 个答案: