如何访问随机子女Firebase DataBase ..？

是否有任何可能的方式来产生从儿童的孩子的结果就像我在单个问题上寻找多个答案。如何访问随机子女Firebase DataBase ..？

"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。！想要做这样的事情！

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();

它会使性能较慢我在寻找一些东西更快的使用！

寻找这样的事情

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

来源

2017-03-17 Atif AbbAsi

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，虽然这将起作用，但我强烈建议您更改数据模型以使此类查询更具可伸缩性。由于答案属于问题，您应该对该层次结构进行建模。虽然你不应该搭配的问题和答案，你应该考虑下这个问题ID造型答案：

"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" : { 
    "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", 
    } 
    } 
}

通过这样的结构，你可以得到Q1的答案有直接查找，而不是一个查询（在每个增长列表中）：

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()); 
     } 
    } 
    ...

来源

2017-03-17 14:11:51

如何访问随机子女Firebase DataBase ..？

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