在检测到仅仅子节点值的变化时访问父对象

I have an Order node and a Status key under that. I am looking for changes in the Status’s value and if there’s any change detected, I have to read the parent Order Node.

我有一个Order节点和一个Status键。我正在寻找状态值的变化，如果检测到任何变化，我必须阅读父订单节点。

The key point is I do not want to listen to changes in the Order node. But just the Status under the Order node. What is the most optimum way to do this? Is it good to have a listener inside another listener? Here's my code:

关键是我不想听Order节点中的更改。但只是Order节点下的Status。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) {

        }

    });

And the JSON:

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"

  } }

1 个解决方案

#1

Why don't you check status first? You know the value of status at beginning. I think this solution should be optimum way.

你为什么不先检查状态？你知道开始状态的价值。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) {}
});