使用swift从firebase字典中删除值，在客户端阻止的用户

Question

我的数据库结构是这样的;

 "blockByUser" : {
  "pcAkkvLY1TYseqk04sISUqop3Wt1" : {
    "7OYw2AtvZ7hxprFiX2e1LOn1DWs2" : true,
    "W4uaW1pOtkYUMh1jTJJVXQu0u6f1" : true
  }
 }

"users" : {
   "Gn0SwQOmUvNkAFeg0YpGax75cpz2" : {
     "blocked" : {
       "pcAkkvLY1TYseqk04sISUqop3Wt1" : true
     },
     "capacity" : "NO",
     "country" : "Netherlands",
     "email" : "katnl"
   },
   "iDlNUNNAsiN0JmO8bEdYAdANcn62" : {
     "blocked" : {
       "Gn0SwQOmUvNkAFeg0YpGax75cpz2" : true
     },
     "capacity" : "NO",
     "country" : "Netherlands",
     "email" : "dal"
   },
   "pcAkkvLY1TYseqk04sISUqop3Wt1" : {
     "capacity" : "NO",
     "country" : "Netherlands",
     "email" : "test",
   }
 }

我现在必须在客户端进行过滤，从blockedByUser中删除密钥，因此我有2个词典，其中一个完整的＆＃39;用户列表和一个blockedByUsers，现在我遇到了更新我的collectionView的问题，因为firebase数据是异步的，我不知道如何让它像这样工作：

func fetchBlockedUsers() {

        print("Fetching blocked users..")

        let ref = FIRDatabase.database().reference().child("blockedByUser").child(currentUserUID)
        ref.observe(.value, with: { (snapshot) in
            guard let dictionaries = snapshot.value as? [String: Any] else { return }

            self.users.removeAll()

            let blocked = dictionaries

            let ref = FIRDatabase.database().reference().child("users")
            ref.observeSingleEvent(of: .value, with: { (snapshot) in
                guard let dictionaries = snapshot.value as? [String: Any] else { return }

                var dict = dictionaries
                for block in blocked {
                    dict.removeValue(forKey: block.key)
                }


                dict.forEach({ (key, value) in
                    guard let userDictionary = value as? [String: Any] else { return }

                    let user = UserModel(uid: key, dictionary: userDictionary)
                    self.users.append(user)
                })

                self.collectionView?.reloadData()

            }) { (err) in
                print("Failed to fetch users for search:", err)
            }

        }) { (err) in
            print("Failed to fetch users for search:", err)
        }

    }

但也许最好将数据扇出并使用firebase功能来管理数据？