How to get all data from a collection that is inside every collection?-CodePudding

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.

CodePudding user response：

You will have to iterate over each teacher in order to fetch all students from the student collection within the teacher document.

See examples from the offical documentation:

https://firebase.google.com/docs/firestore/query-data/get-data

CodePudding user response：

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;
  }