Question 119647 in Firebase Question posted in
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Firebase – How to get all data from a collection that is inside every collection?

Let me say I have ‘teacher’ collection inside ‘teacher’ collection I have ‘student’ collection in Firebase, I need to display every student of every teacher in a list.
I know I can create separate student collection linking teacher id, but this is the scenario I need to work with.
Please help me how can I get every student using FirebaseFirestore query.

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3

Answers


  1. 0

    To achieve this you will query all the teachers and then all the students inside each teacher. I have implemented so I am sharing my experience with you.
    First of all make two models TeacherModel and StudentModel with json serialization for your ease. I have created dummy models you can add your fields in models.

    class TeacherModel {
  TeacherModel({
    this.students,
  });

  factory TeacherModel.fromJson(Map<String, dynamic> json) {
    /// implement from json
    return TeacherModel(students: []);
  }

  /// all the properties of teacher
  List<StudentModel>? students;

  Map<String, dynamic> toJson() => {};
}

class StudentModel {
  StudentModel();

  /// all the properties of student
  factory StudentModel.fromJson(Map<String, dynamic> json) {
    return StudentModel();
  }

  Map<String, dynamic> toJson() => {};
}

    After creating models you have two options.

    1- Get all data in a stream as following.

      static Stream<List<TeacherModel>> getStreamData() async* {
    final firestore = FirebaseFirestore.instance;
    var allTeachers = <TeacherModel>[];
    final result = firestore.collection('teachers').snapshots();
    await for (final r in result) {
      final teacherDocs = r.docs;
      for (final teacherDoc in teacherDocs) {
        final students = (await firestore
                .collection('teachers/${teacherDoc.id}/students')
                .get())
            .docs
            .map((e) => StudentModel.fromJson(e.data()))
            .toList();
        final teacher = TeacherModel.fromJson(teacherDoc.data());
        teacher.students = students;
        allTeachers.add(teacher);
        yield allTeachers;
      }
    }
  }

    2- Get all data in future as following.

    static Future<List<TeacherModel>> getFutureData() async {
    final firestore = FirebaseFirestore.instance;
    var allTeachers = <TeacherModel>[];
    final result = (await firestore.collection('teachers').get()).docs;
    for (final r in result) {
      final students =
          (await firestore.collection('teachers/${r.id}/students').get())
              .docs
              .map((e) => StudentModel.fromJson(e.data()))
              .toList();
      final teacher = TeacherModel.fromJson(r.data());
      teacher.students = students;
      allTeachers.add(teacher);
    }
    return allTeachers;
  }
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  2. 0

    What you’re looking for is known as a collection group query, which allows you to read/query documents from all collections with a specific name.

    Based on the documentation:

    db
    .collectionGroup("student")
    .get()
    .then(
      (res) => print("Successfully completed"),
      onError: (e) => print("Error completing: $e"),
    );
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  3. 0

    I was researching a solution and you have to get creative like how @Sparko recoommends. In the firestore docs they say this:

    "The listCollections() method of the Cloud Firestore server client libraries lists all subcollections of a document reference.

    Retrieving a list of collections is not possible with the mobile/web client libraries. You should only look up collection names as part of administrative tasks in trusted server environments. If you find that you need this capability in the mobile/web client libraries, consider restructuring your data so that subcollection names are predictable."

    This is also a possible work around

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