How to get documents in firestore, whose document IDs are stored in the list?, i.e bring only those documents…?

问题

I have a list that contains the document Ids of a particular collection "users", and I want to get documents only present in this list, and these documents are in "users" collection as mention before.

Code:

  getUsers() async
     {
       double radius = 0.3;
      String field = "GeoPosition";
       print(currentUser.point.longitude);
       GeoFirePoint center = geo.point(latitude: currentUser.point.latitude,  longitude: currentUser.point.longitude);
        var collectionRef = Firestore.instance.collection('user_locations').document(currentUser.pincode)  .collection('Users_complete_address_and_geopoint');
        this.stream =  geo.collection(collectionRef: collectionRef).within(center: center, radius: radius, field: field, strictMode: false);   
        Future<List<certainrangeusers>> users1 =  stream.first.then(
        (documents) => documents.map((doc) => certainrangeusers(
         id: doc['userPhone'],
         )
        ).toList());  
         users1.then((val) async{
        QuerySnapshot snapshot = await  Firestore.instance.collection('users').where('id', isEqualTo: val.first.id).getDocuments();
         List<User> users = snapshot.documents.map((doc) =>  User.fromDocument(doc)).toList();
        setState(() {
         this.users = users;
          });
       });
   }

Firebase Structure: Click here for the firebase structure

Code In image format:

Click here for the image

1. In orange box, "users1" is a list having document IDs...of users 10km users
2. In the pink box, we r using the value of the list...
3. In the green box, we need to pass the document ids present in the above list...

P.s: I am using "val.first.id" just to bring the document present at first in the list........But I need to bring every document present in that list...so that's a point I have struck...

回答1:

Here how to search for all documents from the list id

instead of:

await  Firestore.instance.collection('users').where('id', isEqualTo: 
 val.first.id).getDocuments();

use this:

await  Firestore.instance.collection('users').where('id', whereIn: 
 val).getDocuments();

Since you have a list of certainchangeuser, do this to get the ids.

users1.then((val){
  // Get the ids
  List ids = [];
  for (var value in val){
    ids.add(value.id);
  }
  //Then
  QuerySnapshot = await 
    Firestore.instance.collection('users').where('id', 
    whereIn:ids).getDocuments();
....
});

回答2:

You can use a transaction for this purpose. Firestore transactions

来源：https://stackoverflow.com/questions/61584880/how-to-get-documents-in-firestore-whose-document-ids-are-stored-in-the-list-i