java - equalTo ("value","key") 在 Firebase 中的用法？

Question

数据结构如下:

{
  "list" : {
    "-K4YlfoWHZqPyWONv68Y" : {
      ".priority" : -1.449077948445E12,
      "date" : 1449077948445,
      "id" : "0",
      "name" : "Name_0"
    },
    "-K4YlfoWHZqPyWONv68Z" : {
      ".priority" : -1.449077948445E12,
      "date" : 1449077948445,
      "id" : "1",
      "name" : "Name_1"
    },
    "-K4YlfoWHZqPyWONv68_" : {
      ".priority" : -1.449077948445E12,
      "date" : 1449077948445,
      "id" : "0",
      "name" : "Name_2"
    },
    "-K4YlfoWHZqPyWONv68a" : {
      ".priority" : -1.449077948445E12,
      "date" : 1449077948445,
      "id" : "1",
      "name" : "Name_3"
    },
 ...
}

我只需要获取id为“0”的项目；

以下是有效的:

final Firebase ref = new Firebase("https://millezim-test.firebaseio.com/").child("list");

ref.orderByChild("id").equalTo("1").addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot d : dataSnapshot.getChildren()) {
            Model m = d.getValue(Model.class);
        }
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {

        }
});

但不是这个，为什么？

ref.equalTo("1","id").addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot d : dataSnapshot.getChildren()) {
            Model m = d.getValue(Model.class);
        }
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {

        }
});

我是否误解了 equalTo("value","key") 是在不重新排序的情况下使用的？

Answer 1

Firebase documentation for equalTo关于(可选)key 参数的说明:

The child key to start at, among the children with the previously specified priority. This argument is only allowed if ordering by priority.

由于您没有按优先级排序，因此您需要通过显式调用 orderByChild() 来指定 child 。