在检测到仅仅子节点值的变化时访问父对象

Question

我有一个Order节点和一个Status密钥.我正在寻找Status值的变化,如果检测到任何变化,我必须到read父Order节点.

关键是我不想听Order节点的变化.但只是Status在Order节点下.最佳方式是什么？在另一个监听器中有一个监听器是否好？这是我的代码:

 final Query qRef = FirebaseDatabase.getInstance().getReference().child("orders").orderByChild("customerId").equalTo(FirebaseAuth.getInstance().getCurrentUser().getUid())
            .limitToFirst(1);
    qRef.keepSynced(true);

    final DatabaseReference reference = qRef.getRef().child("status");


    reference.addValueEventListener(new ValueEventListener() {

        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {


            DatabaseReference inner = reference.getParent();

            inner.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot parent) {
                    if (parent != null) {
                        Order newOrder = parent.getValue(Order.class);
                        if (newOrder != null) {
                            if (newOrder.getStatus() != null && !newOrder.getStatus().equals("FX_OVER"))
                                processOrder(newOrder);
                        }
                    }
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }

    });

和JSON:

{   "20161010210955" : {
    "createdAt" : {
      "date" : 10,
      "day" : 1,
      "hours" : 21,
      "minutes" : 9,
      "month" : 9,
      "seconds" : 55,
      "time" : 1476113995244,
      "timezoneOffset" : -330,
      "year" : 116
    },
    "customerId" : "npsd3Ldfsdf1x0hsdfsdf2mj14VUA876f2",
    "id" : "20161010210955",
    "status" : "FX_FULL"

  } }

Answer 1

为什么不先检查一下状态呢？你一开始就知道地位的价值。我认为这个解决方案应该是最佳方式。

reference.addValueEventListener(new ValueEventListener() {

    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {

        if("FX_OVER".equals(dataSnapshot.getValue(String.class)) {

            reference.getParent().addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot parent) {
                    // This is a defensive check. I dont know this is necessary.
                    // If status exist, parent must be exist.
                    if (parent.exists()) {
                        Order newOrder = parent.getValue(Order.class);
                        if (newOrder != null) {
                            processOrder(newOrder);
                        }
                    }
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {}
            });
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
});