对如何正确使用http Firebase Cloud Function中的promise感到困惑

Question

我刚开始将云函数与http触发的函数一起用于Firebase，我对如何正确终止该函数感到困惑。我不确定是应该使用res.sendStatus，还是返回promise，或者两者都使用。

我的功能的目标是循环浏览集合"communities"中的几个文档。每个社区都有一个文档集合，我在其中查询具有最高值"hotScore"的文档。然后，我将包含该文档的iOS推送通知发送到某个主题(该给定社区中的所有用户(。

不幸的是，在运行代码时，我遇到了几个错误，例如Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client和Unhandled rejection。我很清楚这是由于我在处理功能终止时的疏忽，尽管到目前为止我已经被我所看到的在线资源弄糊涂了。有人介意看一下我的代码/给我指明正确的方向吗？非常感谢！

exports.sendNotificationTrendingPost = functions.https.onRequest(async (req, res) => {
//Get communities collection from Firestore
return admin.firestore().collection('communities').get().then((communities) => {
var communityPromises = [];
//Loop through each community
communities.forEach((community) => {
let communityID = community.get('communityID');
let communityName = community.get('name');
//Get the post with the highest hotScore
let communityPromise = admin.firestore().collection('communities').doc(communityID).collection('posts').orderBy('hotScore', 'desc').limit(1).get().then((posts) => {
let hottestPost = posts[0];
let postID = hottestPost.get('postID');
let postText = hottestPost.get('text');
let currentDate = Date.now() / 1000;
var message;
//Verify that the hottest post was posted in the past 24 hours
if (hottestPost.get('date') > (currentDate - 86400)) {
//Build the notification text (shortening if too long)
let shortenedPostText = postText.substring(0,60);
var textEnd = '';
if (postText.length > 60) {
textEnd = '...';
}
let notificationText = 'Trending post on ' + communityName + ': ' + shortenedPostText + textEnd;
//Build the push notification
message = {
apns: {
headers: {
'apns-push-type': 'alert'
},
payload: {
aps: {
alert: {
body: notificationText,
},
},
postID: postID,
},
},
topic: communityID
}
}
//Send the message and return the promise
if (message === null) {
return null;
} else {
return admin.messaging().send(message);
}
})
.catch(error => {
console.log(error);
res.status(500).send(error);
})
if (communityPromise !== null) {
communityPromises.push(communityPromise);
}
})
res.sendStatus(200);
return Promise.all(communityPromises);
})
.catch(error => {
console.log(error);
res.status(500).send(error);
})
})

Answer 1

正如samthecodingman所建议的那样，在您的情况下使用async/await要好得多，因为它会简化代码并使其更易于阅读。

下面的更改应该可以达到目的(未经测试(。请注意，我们如何使用社区名称数组将名称从一个循环传递到另一个循环。这是因为，对于Promise.all()，无论完成顺序如何，返回的值都是按传递的Promises的顺序排列的。

exports.sendNotificationTrendingPost = functions.https.onRequest(async (req, res) => {
try {
const db = admin.firestore();
const communitiesQuerySnap = await db.collection('communities').get();
const communityPromises = [];
const communityNames = [];
communitiesQuerySnap.forEach((community) => {
let communityID = community.get('communityID');
let communityName = community.get('name');
communityNames.push(communityName);
communityPromises.push(db.collection('communities').doc(communityID).collection('posts').orderBy('hotScore', 'desc').limit(1).get())
});
const postsQuerySnapArray = await Promise.all(communityPromises);
const messagePromises = [];
postsQuerySnapArray.forEach((postsQuerySnap, index) => {
const hottestPost = postsQuerySnap.docs[0];
const postID = hottestPost.get('postID');
const postText = hottestPost.get('text');
const currentDate = Date.now() / 1000;
let message;
if (hottestPost.get('date') > (currentDate - 86400)) {
//Build the notification text (shortening if too long)
let shortenedPostText = postText.substring(0, 60);
var textEnd = '';
if (postText.length > 60) {
textEnd = '...';
}
const communityName = communityNames[index];  // The two Arrays postsQuerySnapArray and communityName have the same order, because Promise.all keeps the order.
let notificationText = 'Trending post on ' + communityName + ': ' + shortenedPostText + textEnd;
//Build the push notification
message = {
apns: {
headers: {
'apns-push-type': 'alert'
},
payload: {
aps: {
alert: {
body: notificationText,
},
},
postID: postID,
},
},
topic: communityID
}
messagePromises.push(admin.messaging().send(message));
}
})
await Promise.all(messagePromises);
res.status(200).send({ result: "completed" }); // Or res.end()
} catch (error) {
console.log(error);
res.status(500).send(error);
}
});