Question

我正在尝试从出勤集合和学生集合中检索其userUID匹配的每个学生的姓名，即，如果两个用户UID匹配，我想从学生集合中返回与userUID关联的名称。我正在查询出勤表。

这是我的代码：

public void viewAttendance(View v) {
    attendanceRef2.orderBy("sessionID", Query.Direction.ASCENDING)
            .get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
        @Override
        public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
            String data = "";

            for (QueryDocumentSnapshot documentSnapshot : queryDocumentSnapshots) {
                Attendance attendance = documentSnapshot.toObject(Attendance.class);
                Student studentName = documentSnapshot.toObject(Student.class);

                String sessionID = attendance.getSessionID();
                String studentID = attendance.getUserUID();
                String attendanceUID = studentName.getUserUID();
                String name;

                if (studentID.equals(attendanceUID)){

        name = studentName.getName();
                    data+= "Session ID: " + sessionID + "\n" + "Student Name: " + name + "\n\n";
                }
            }
            textViewData.setText(data);
        }
    });
}

修改后的代码

public void viewAttendance(View v) {
    attendanceRef2.orderBy("sessionID", Query.Direction.ASCENDING)
            .get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
        @Override
        public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
            String data = "";

            for (QueryDocumentSnapshot documentSnapshot : queryDocumentSnapshots) {
                Attendance attendance = documentSnapshot.toObject(Attendance.class);
                Student studentName = documentSnapshot.toObject(Student.class);

                String sessionID = attendance.getSessionID();
                String attendanceUID = attendance.getUserUID();
                String studentUID = studentName.getUserUID();
                final String name = "";

                if (attendanceUID.equals(studentUID)){
                    db.collection("Student").document("name").get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
                        @Override
                        public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                            textViewData.setText(name);
                        }
                    });

                }
                data+= "Session ID: " + sessionID + "\n" + "Student Name: " + name + "\n\n";
            }
            textViewData.setText(data);
        }
    });
}

Answer 1

您越来越近了。您需要加载两个文档：

出勤信息
学生的用户信息

由于用户名来自第二个文档，因此只能在加载第二个文档后调用DocumentSnapshot.toObject（因此，在第二个侦听器的onComplete或onSuccess回调中）。像这样：

public void viewAttendance(View v) {
  attendanceRef2.orderBy("sessionID", Query.Direction.ASCENDING)
        .get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
    @Override
    public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
        String data = "";

        for (QueryDocumentSnapshot documentSnapshot : queryDocumentSnapshots) {
            Attendance attendance = documentSnapshot.toObject(Attendance.class);

            String sessionID = attendance.getSessionID();
            String attendanceUID = attendance.getUserUID();
            String studentUID = studentName.getUserUID();

            if (attendanceUID.equals(studentUID)){
                db.collection("Student").document(studentUID).get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                        Student studentName = task.getResult().toObject(Student.class);
                        textViewData.setText(studentName);
                        // Or maybe: textViewData.setText(studentName.getName());

                        data+= "Session ID: " + sessionID + "\n" + "Student Name: " + studentName + "\n\n";
                        textViewData.setText(data);
                    }
                });

            }
        }
    }
  });
}

尝试根据两个匹配的集合的UID从一个集合中检索字段

1 个答案: