firebase - 按整数对文档进行排序Firestore Kotlin

Question

我想按img降序对文档进行排序。
我试图在Firebase控制台中添加索引。这是“索引”标签中的屏幕截图:

这是我的数据库结构:


这是我的代码:

db.collection("images").whereEqualTo("user", uid).orderBy("img", Query.Direction.DESCENDING).get()
    .addOnSuccessListener {
        if (it.isEmpty) {
            Log.i("Image", "Sorry, no image")
        } else {
            for (task in it) {
                Log.i("Image", task.get("img").toString())
            }
        }
    }

这是日志:

I/Image: 2
I/Image: 1
I/Image: 3
I/Image: 4
I/Image: 6
I/Image: 7

我究竟做错了什么？

Answer 1

请注意，如documentation所述，在您所遇到的行为背后可能有两种解释:

1. If you have a filter with a range comparison (<, <=, >, >=), your first ordering must be on the same field

2. You cannot order your query by any field included in an equality (=) or in clause.

基于文档中提供的以下代码段:

citiesRef.whereGreaterThan("population", 100000).orderBy("population").limit(2)

您可以尝试以下操作(但是由于2，我不确定是否可以使用):

db.collection("images").whereEqualTo("user", uid).orderBy("user").orderBy("img", Query.Direction.DESCENDING).get()
    .addOnSuccessListener {
        if (it.isEmpty) {
            Log.i("Image", "Sorry, no image")
        } else {
            for (task in it) {
                Log.i("Image", task.get("img").toString())
            }
        }
    }