How to loop through Instance of '_MapStream>>'?

Question

  static List categoryList() {
    final categorySnapshots = FirebaseFirestore.instance
        .collection('categories')
        .orderBy('name')
        .snapshots();

    List categories = [];
    categorySnapshots.map((snapshot) => snapshot.docs.map((doc) {
          print(snapshot.toString());
          categories.add(doc.data()['name']);
        }));

    print(categories);
    return categories;
  }

Categories is empty. How to populate it with the data from snapshots?

It says "The getter 'data' isn't defined for the type 'QuerySnapshot>'" — Dee Mee, Jul 10 '22 at 12:57
`snapshots()` will return a stream, so you should use it when you wan't to listen to realtime updates. If you want to make a one-time query, use `get()` instead of `snapshots()` and `await` the result. — Peter Koltai, Jul 10 '22 at 13:18

Joel Mathew · Answer 1 · 2022-07-12T16:05:59.833

0

Using the below code might help

you can convert the snapshot to Map<String,dynamic> by using the following function:

 static Post fromSnap(DocumentSnapshot snap) {
var snapshot = snap.data() as Map<String, dynamic>; 
}

edited Jul 12 '22 at 16:05

answered Jul 10 '22 at 16:26

Joel Mathew

14
3

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Jul 11 '22 at 15:46

score 0 · Answer 2 · answered Jul 10 '22 at 17:27

I added a new collection called "school", there're two items added inside the document.

  void getMessagesTest() async{
    QuerySnapshot querySnapshot = await _firestore.collection('school').orderBy('age',descending: true).get();
    final allData = querySnapshot.docs.map((doc) => doc.data()).toList();
    print(allData);
  }

I used my code, and it works. Could you please remove ".where" and try it again?

You could chain where and orderBy together. Please see my code below. Reference link => Using Where and Order by different fields in Firestore query

  void getMessagesTest() async{
    QuerySnapshot querySnapshot = await _firestore.collection('school').orderBy('age', descending: true).where('age', isGreaterThan: 17).get();
    final allData = querySnapshot.docs.map((doc) => doc.data()).toList();
    print(allData);
  }

How to loop through Instance of '_MapStream>>'?

2 Answers2