Observable 类型上不存在属性“then” <querysnapshot<documentdata> &gt; </querysnapshot<documentdata>

Question

db.collection("cities").get()
  .then(function(querySnapshot) {
    querySnapshot.forEach(function(doc) {
      // doc.data() is never undefined for query doc snapshots
      console.log(doc.id, " => ", doc.data());
  });

I'm trying to read multiple document of a collection, but getting error on then. Please help me to sort out this.

Answer 1

If you want to treat is as a promise, you can convert it to a promise. This isn't a hack, once there's only one emission being produced by get() . But Firebase expected you to deal with the stream that's coming out from get() though. Anyway, to convert it to a promise:

db.collection("cities").get().toPromise()
  .then((querySnapshot: QuerySnapshot<DocumentData>) => {
    querySnapshot.forEach((doc: any) => {
      // doc.data() is never undefined for query doc snapshots
      console.log(doc.id, " => ", doc.data());
  });

If you decide to deal with the streaming coming out from get() , as Firebase API expected you to:

db.collection("cities").get()
  .subscribe((querySnapshot: QuerySnapshot<DocumentData>) => {
    querySnapshot.forEach((doc: any) => {
      // doc.data() is never undefined for query doc snapshots
      console.log(doc.id, " => ", doc.data());
  });

[UPDATE] 1: Based on the docs, there's a new API for getting the snapshots, using the onSnapshot method:

db.collection("cities")
  .onSnapshot((querySnapshot: QuerySnapshot<DocumentData>) => {
    querySnapshot.forEach((doc: any) => {
      // doc.data() is never undefined for query doc snapshots
      console.log(doc.id, " => ", doc.data());
  });