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?

CodePudding user response：

Using the below code might help

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

CodePudding user response：

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);
  }