[英]How do I use a document's field from one collection to retrieve another document field from a different collection?
Here is how my database is structured: challenges table & users table这是我的数据库的结构:挑战表和用户表
Here is the error I'm getting: error image这是我得到的错误:错误图片
I want to use the "created_by" field which is also a document id for the users table, where I want to retrieve both the display name and the photo URL.我想使用“created_by”字段,它也是用户表的文档 ID,我想在其中检索显示名称和照片 URL。
I'm not all the way sure how promises work and I have a feeling that is why I'm struggling, but the code I have thus far is below:我并不完全确定 Promise 是如何工作的,我有一种感觉,这就是我在挣扎的原因,但到目前为止我所拥有的代码如下:
Data Retrieval:数据检索:
UsersDao.getUserData(ChallengesDao.getChallenges().then(result => {return result['author'][0]})).then(result => {console.log(result)})
Challenges DAO:挑战 DAO:
export default class ChallengesDao {
static async getChallenges() {
const db = require('firebase').firestore();
// const challenges = db.collection('challenges').limit(number_of_challenges)
// challenges.get().then(())
const snapshot = await db.collection('challenges').get()
const names = snapshot.docs.map(doc => doc.data().name)
const createdBy = snapshot.docs.map(doc => doc.data().created_by)
const highScores = snapshot.docs.map(doc => doc.data().high_score.score)
return {challengeName: names, author: createdBy, score: highScores}
}
Users DAO:用户DAO:
const db = require('firebase').firestore();
export default class UsersDao {
static async getUserData(uid: string) {
let userData = {};
try {
const doc = await db
.collection('users')
.doc(uid)
.get();
if (doc.exists) {
userData = doc.data();
} else {
console.log('User document not found!');
}
} catch (err) {}
return userData;
}
}
You're getting close.你越来越近了。 All that's left to do is to call getUserData
for each UID you get back from getChallenges
.剩下要做的就是为从getChallenges
返回的每个 UID 调用getUserData
。
Combining these two would look something like this:将这两者结合起来看起来像这样:
let challenges = await getChallenges();
let users = await Promise.all(challenges.author.map((uid) => getUserData(uid));
console.log(challenges.challengeName, users);
The new thing here is Promise.all()
, which combines a number of asynchronous calls and returns a promise that completes when all of them complete.这里的新东西是Promise.all()
,它结合了许多异步调用并返回一个 promise ,当它们全部完成时完成。
Your code looks a bit odd to me at first, because of the way you return the data from getChallenges
.你的代码起初对我来说有点奇怪,因为你从getChallenges
返回数据的方式。 Instead of returning three arrays with simple values, I'd recommend returning a single array where each object has three values:我建议不要返回三个 arrays 的简单值,而是返回一个数组,其中每个 object 具有三个值:
static async getChallenges() {
const db = require('firebase').firestore();
const snapshot = await db.collection('challenges').get();
const challenges = snapshot.docs.map(doc => { name: doc.data().name, author: doc.data().created_by, score: doc.data().high_score.score });
return challenges;
}
If you then want to add the user name to each object in this array, in addition to the UID that's already there, you could do:如果您想将用户名添加到此数组中的每个 object 中,除了已经存在的 UID 之外,您可以执行以下操作:
let challenges = await getChallenges();
await Promise.all(challenges.forEach(async(challenge) => {
challenge.user = await getUserData(challenge.author);
});
console.log(challenges);
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