将两个以上的 collections 从 Firestore 复制到另一个集合不起作用

Question

So I have four collections in my firestore database:

1. EnglishQuestions
2. MathQuestions
3. ScienceQuestions
4. DzongkhaQuestions

I am trying to copy all the data from those collections and put it under one collection for each user. So it would look like this.

1. username(collection)
   • MathQuestions (doc) - Questions (collection)
   • EnglishQuestions (doc) - Questions (collection)
   • ScienceQuestions (doc) - Questions (collection)
   • DzongkhaQuestions (doc) - Questions (collection) However, when I am trying to do this, it act weirdly in the sense that sometimes, all the four collections gets copied in the username collection but other times only the first two collections or the first collection gets copied.

Before I had the part where you call the database for each collection one after another. Since that didn't work I tried to make each call a function of its own as seen below. Sadly that doesn't work as well. Any help would be greatly appreciated.

After taking @ralemos's suggestion, it still doesn't work but the new code looks like the following.

    fire
      .auth()
      .createUserWithEmailAndPassword(this.state.email, this.state.password)
      .then((u) => {
        let user = fire.auth().currentUser;
        console.log(user);
        if (user != null) {
          user
            .updateProfile({
              displayName: this.state.name,
            })
            .then((r) => {
              let db = fire.firestore();
              let data = {
                name: this.state.name,
                email: this.state.email,
                college: this.state.college,
                dzongkhag: this.state.dzongkhag,
              };
              db.collection(this.state.email).doc("UserProfile").set(data);
              this.copyMathDatabase();
            });
        }
      });
  }
  copyMathDatabase() {
    let db = fire.firestore();
    db.collection("Questions")
      .get()
      .then((snapshot) => {
        snapshot.forEach((doc) => {
          db.collection(this.state.email).doc("MathQuestions").collection("Questions").doc(doc.id).set({
            Category: doc.data().Category,
            Choice: doc.data().Choice,
            CorrectAnswer: doc.data().CorrectAnswer,
            IsCorrectAnswer: doc.data().IsCorrectAnswer,
            IsWrongAnswer: doc.data().IsWrongAnswer,
            Question: doc.data().Question,
            UserHasNotResponded: doc.data().UserHasNotResponded,
            Marked: doc.data().Marked,
          });
          console.log("Math Questions: ", doc.id);
        });
        this.copyEnglishDatabase();
        console.log(" Done copying the Math database ");
      });
  }

  copyEnglishDatabase() {
    let db = fire.firestore();
    db.collection("EnglishQuestions")
      .get()
      .then((snapshot) => {
        snapshot.forEach((doc) => {
          db.collection(this.state.email).doc("EnglishQuestions").collection("Questions").doc(doc.id).set({
            Category: doc.data().Category,
            Choice: doc.data().Choice,
            CorrectAnswer: doc.data().CorrectAnswer,
            IsCorrectAnswer: doc.data().IsCorrectAnswer,
            IsWrongAnswer: doc.data().IsWrongAnswer,
            Question: doc.data().Question,
            UserHasNotResponded: doc.data().UserHasNotResponded,
            Marked: doc.data().Marked,
            Passage: doc.data().Passage,
            isPassageQuestion: doc.data().isPassageQuestion,
          });
          console.log("English Questions: ", doc.id);
        });
       
        console.log("Done copying the English database");
      });
  }

Answer 1

Remember, many/most Firestore calls return a promise - which means the result of an operation to be returned later, possibly much later. Just putting one call after the other does NOT mean one will wait for the other - that isn't at all what promises do. You may have seen some code that uses async/await, which LOOK like they wait for each other - but it's just "syntactic sugar" (ie makes it look good) that hides the fact that there are STILL promises "behind the scenes".

For your example, I would do the following:

copyMathDatabase() {
    let db = fire.firestore();
    return db.collection("Questions")
    ...
}

copyEnglishDatabase() {
    let db = fire.firestore();
    return db.collection("EnglishQuestions")
    ...
}

Note the "return" - each function now returns the PROMISE of a result, which will happen sometime later. Then, in your auth function area:

  fire
      .auth()
      .createUserWithEmailAndPassword(this.state.email, this.state.password)
      .then((u) => {
        let user = fire.auth().currentUser;
        console.log(user);
        if (user != null) {
          user
            .updateProfile({
              displayName: this.state.name,
            })
            .then((r) => {
              let db = fire.firestore();
              let data = {
                name: this.state.name,
                email: this.state.email,
                college: this.state.college,
                dzongkhag: this.state.dzongkhag,
              };
              return db.collection(this.state.email).doc("UserProfile").set(data);
            })
            .then(() => {
              return this.copyMathDatabase();
             })
            .then(() => {
              return this.copyEnglishDatabase();
            };
        }
      });
  }

note - the result of the.set() returns a PROMISE to be completed when it is done; .then() waits for that promise then executes copyMathDatabase(), which returns a PROMISE to be completed when it is done; .then() waits for that promise then executes copyEnglishDatabase(), which returns a PROMISE to be completed when it is done.

This question shows you have very very little understanding of exactly what promises are - and that understanding is absolutely critical and necessary to using Firestore. You need to go and teach yourself promises in detail before you continue. You should also learn what the aync/await syntax is, and what it actually does. This is NOT the place for you to learn these things.

Answer 2

This is very likely to be a synchronicity issue caused by calling copyMathDatabase() and copyEnglishDatabase() , which are both asynchronous, in sequence, try changing that block of your code to the following:

db.collection(this.state.email).doc("UserProfile").set(data).then(() =>{
    this.copyMathDatabase().then(() => {
        this.copyEnglishDatabase();
    });
});

This way your are forcing your code to be executed in the proper order and mitigating errors, and this should fix the issue you are facing.