如何访问随机子Firebase数据库..?

时间:2017-03-17 12:01:44

标签: java android firebase firebase-realtime-database firebase-storage

是否有任何可能的方法来生成孩子的孩子的结果 喜欢我在单个问题上寻找多个答案。!

"questions" : {
    "Q1(Random ID )" : {
      "description" : "Deail of Question",
      "idQuestion" : "Q1",
      "time" : "17 Mar 2017 16:18:12",
      "title" : "Title Of Question",
      "user_id" : "bXCeW6jfidbHuMCCCMkDGWcGZRS2"
    },
{
  "Answer" : {
    "81d19e85-8c6c-4824-9fb1-61a7cd316e32" : {
      "dateTime" : "17 Mar 2017 16:22:17",
      "Answer" : "Answer",
      "ProfessorId" : "da587c89-f001-43f2-984d-e6dbac491acc",
      "questionId" : "Q1"
    },
    "e2ec0556-4420-4d2f-b346-0b5cebeb1ebe" : {
      "dateTime" : "17 Mar 2017 16:55:27",
      "Answer" : "Answer 2 on Question 1",
      "answerId" : "0d20d6df-907d-4133-be53-ca6acf6c2ad1",
      "questionId" : "Q1"
    }
  },

随机生成的节点。 ! 我想做这样的事情。!

mdatabaseReference.child("Answer").child(* Here Im Using "*" Like we used to do in SQl to get all data I knw its not a SQL but its just for conecpt).equalTo(QID).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {

                if (Answer_List.size() > 0)
                    Answer_List.clear();


                for (DataSnapshot postsnapshot : dataSnapshot.getChildren()) {

而不是使用postSnapshot.getKey().equals("QID")

    if(postSnapshot.getKey().equals("QID"))  
 Answertext = postSnapshot.getValue().toString();

这会让性能变得更慢,我正在寻找更快的东西。!

寻找类似的东西

 mdatabaseReference.child("Answer").child("*").getKey().equals(QID).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {

1 个答案:

答案 0 :(得分:1)

您正在寻找Firebase Database queries

mdatabaseReference
  .child("Answer")
  .orderByChild("questionId")
  .equalTo("Q1")
  .addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
      for (DataSnapshot answerSnapshot: dataSnapshot.getChildren()) {
        System.out.println(answerSnapshot.child("Answer").getValue());
      }
    }
    ...

但是,虽然这样可行,但我强烈建议您更改数据模型,以使此类查询更具可扩展性。由于答案属于问题,因此您应该对该层次结构建模。虽然不应该混合问题和答案,但考虑在问题ID下对答案进行建模:

"questions" : {
    "Q1(Random ID )" : {
      "description" : "Deail of Question",
      "idQuestion" : "Q1",
      "time" : "17 Mar 2017 16:18:12",
      "title" : "Title Of Question",
      "user_id" : "bXCeW6jfidbHuMCCCMkDGWcGZRS2"
    },
}
"Answer" : {
  "Q1": {
    "81d19e85-8c6c-4824-9fb1-61a7cd316e32" : {
      "dateTime" : "17 Mar 2017 16:22:17",
      "Answer" : "Answer",
      "ProfessorId" : "da587c89-f001-43f2-984d-e6dbac491acc",
    },
    "e2ec0556-4420-4d2f-b346-0b5cebeb1ebe" : {
      "dateTime" : "17 Mar 2017 16:55:27",
      "Answer" : "Answer 2 on Question 1",
      "answerId" : "0d20d6df-907d-4133-be53-ca6acf6c2ad1",
    }
  }
}

通过这种结构,您可以通过直接查找而不是查询(在每个增长列表中)获得Q1的答案:

mdatabaseReference
  .child("Answer")
  .child("Q1")
  .addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
      for (DataSnapshot answerSnapshot: dataSnapshot.getChildren()) {
        System.out.println(answerSnapshot.child("Answer").getValue());
      }
    }
    ...