对于有效的文档参考，DocumentSnapshot始终为null

Question

我正在Firestore上存储结构化数据，我想获取特定嵌套文档的数据，并且该数据必须是实时的，因为数据是实时更新的。

这是Firestore中的结构：

所以基本上，我有以下路径：

collection(Users).document(23).collection(orders).document(16)
or
/Users/23/orders/21

..我想获取“订单”集合的文档16的数据。

---

这是代码

  class FireStoreMapActivity{
  DocumentReference  doc;


    void getData(){

    doc = FirebaseFirestore.getInstance()
                    .collection("Users")
                    .document(23 + "")
                    .collection("orders")
                    .document(21 + "");

     doc.addSnapshotListener(this, (documentSnapshot, e) -> {

                if (documentSnapshot != null) {
                    if (documentSnapshot.exists()) {
                        List<String> images = (List<String>) documentSnapshot.get("images");
                        Log.e(">>>>>>>>>>> size => ", locHistory.size() + " ");

                    } else {
                        Log.e(">>>>>>>> error ", " documentSnapshot != exists");
                    }
                } else {
                    Log.e(">>>>>>>> error ", " documentSnapshot = null");
                }
            });
  }
}

---

但是每次都会出现空日志 Log.e(">>>>>>>> error ", " documentSnapshot = null");

更新

好吧，在打印异常后，这似乎是一个权限错误！

com.google.firebase.firestore.FirebaseFirestoreException: PERMISSION_DENIED: Missing or insufficient permissions.

这是我的规则集

service cloud.firestore {
  match /databases/{database}/documents {
    match /Users/{document=**} {
      allow read, write: if request.auth.uid != null;
    }
  }
}

但是如何通知Firestore我实际上是经过身份验证的用户！！？

Answer 1

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---

从您的更新来看，您的规则似乎只需要经过身份验证的用户，但是服务器会根据这些规则拒绝您的侦听器。这意味着您未登录，或者至少在尝试从Firestore读取时未登录。

鉴于您共享的代码没有显示任何有关身份验证的信息，因此很难多说。不过，如果您想验证，请在致电e之类的addSnapshotListener之类的用户之前登录。