JavascriptPromise-第二個然后在第一個之前運行

我創建了一個簡單的腳本來獲取 Strava 活動并將它們保存到 mongoDB，但我遇到了以下問題：

在獲取和提交活動之前，我的資料庫連接斷開。以下代碼輸出：

const stravaApi = require('strava-v3');
const mongoose = require('mongoose');
const Activity = require('./models/Activity');

mongoose.connect(process.env.DB_CONNECTION, () => console.log('connected to DB'))

strava = new stravaApi.client(accessToken)
strava.athlete.listActivities({per_page: 2})
        .then(payload => {
            let activities = []
            for (let strava_activity of payload) {
                const activity = new Activity({
                        activityId: strava_activity['id'],
                        name: strava_activity['name'],
                        date: strava_activity['start_date'],
                        type: strava_activity['type'],
                        distance: strava_activity['distance']
                })
                activity.save()
                    .then(data => {
                        console.log(`Activity from date ${strava_activity['start_date']} saved to DB`);
                     })
                    .catch(err => {
                        console.log(err)
                    })
            }
        })
        .then(() => {
            console.log('Start disconnect')
            mongoose.disconnect().then(() => {
                console.log("DB disconnected successfully")
            })
        })
        .catch(err => {
            console.log(err)
        })

輸出

connected to DB
DB disconnected successfully
(Error message)
(Error message)

uj5u.com熱心網友回復：

回圈運行的then-callbackfor不回傳承諾，因此then鏈接到它的 -callback 將在下一個微任務中啟動。

該for回圈內的承諾應該朝著then-callback 將回傳的承諾構建，但回傳的承諾activity.save().then(...)被忽略。

當您使用async await語法時，事情變得更容易：

(async function () {
    await mongoose.connect(process.env.DB_CONNECTION);
    console.log('connected to DB');

    const strava = new stravaApi.client(accessToken);
    const payload = await strava.athlete.listActivities({per_page: 2});
    for (const {id, name, start_date, type, distance} of payload) {
        const activity = new Activity({
            activityId: id,
            name,
            date: start_date,
            type,
            distance
        });
        await activity.save();
        console.log(`Activity from date ${start_date} saved to DB`);
    }
    console.log('Start disconnect')
    await mongoose.disconnect();
    console.log("DB disconnected successfully");
})().catch(console.log);

uj5u.com熱心網友回復：

嘗試僅在承諾的所有實體都結束時傳遞資料庫斷開連接，如下所示：

strava.athlete.listActivities({per_page: 2})
    .then(payload => {
        let activities = []
        for (let strava_activity of payload) {
            const activity = new Activity({
                    activityId: strava_activity['id'],
                    name: strava_activity['name'],
                    date: strava_activity['start_date'],
                    type: strava_activity['type'],
                    distance: strava_activity['distance']
            })
            activity.save()
                .then(data => {
                    console.log(`Activity from date ${strava_activity['start_date']} saved to DB`);
                 })
                .catch(err => {
                    console.log(err)
                })
        }
    })
    .then(() => {})
    .catch(err => {
        console.log(err)
    }).finally(() => {
        console.log('Start disconnect')
        mongoose.disconnect().then(() => {
            console.log("DB disconnected successfully")
        })
    })

這樣他們只會在咨詢完成后斷開連接

標籤：javascript 节点.js MongoDB es6-promise

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