如何通过嵌套的Firebase数据循环快速填充数组

Question

我想通过从一个Firebase节点获取值并使用这些值从另一个Firebase节点获取信息来填充数组。我该怎么办？

[请帮助我，stackoverflow神。我快要哭了。

这是我的Firebase数据库的外观：

{
              "MainTree" : {
                "subTree1" : {
                  "JiRtkpIFLVFNgmNBpMj" : {
                    "PiRterKFLVFNgmFFFtu" : "PiRterKFLVFNgmFFFtu"
                    "TfRterKFLVFNgmFGFre" : "TfRterKFLVFNgmFGFre",
                    "X4RterKFLVFNgmaDFca" : "X4RterKFLVFNgmaDFca"
                    }
                  },
                "subTree2" : {
                    "PiRterKFLVFNgmFFFtu" : {
                    "username" : "user1",
                    "uid" : "PiRterKFLVFNgmFFFtu"
                    },
                    "TfRterKFLVFNgmFGFre" : {
                    "username" : "user2",
                    "uid" : "TfRterKFLVFNgmFGFre"
                    },
                    "X4RterKFLVFNgmaDFca" : {
                    "username" : "user3",
                    "uid" : "X4RterKFLVFNgmaDFca"
                    }
                }
                }
            }

我的通话功能

fetchAllBookmarks(uid: "JiRtkpIFLVFNgmNBpMj", completion: { (userdata) in
                print("fetched all userdata! : ",userdata)

            }) { (err) in
                print("you failed yet again")
            }

我的功能

func fetchAllInformation(uid: String, includeCurrentUser: Bool = true, completion: @escaping ([UserData]) -> (), withCancel cancel: ((Error) -> ())?) {

    let ref = Database.database().reference().child("MainTree").child("subTree1").child(uid)
    ref.observeSingleEvent(of: .value, with: { (snapshot) in

        if snapshot.exists(){
            guard let dictionaries = snapshot.value as? [String: Any] else {
                completion([])
                return
            }
            var Values = [UserData]()
            let group = DispatchGroup()
            dictionaries.forEach({ (key, value) in
                group.enter()
                let ref = Database.database().reference().child("MainTree").child("subTree2").child(key)
                ref.observeSingleEvent(of: .value, with: { (snapshot) in
                    guard let userDictionary2 = snapshot.value as? [String: Any] else { return }
                    let user = UserData(dictionary: userDictionary2)
                    Values.append(user)
                }) { (err) in
                    print("Failed to fetch all user data from database:", (err))
                    cancel?(err)
                }
            })
            group.notify(queue: .main) {
                print("loop done")
                completion(bookmarkedUsers)
            }
        }
    }) { (err) in
        print("Failed to fetch all data from database:", (err))
        cancel?(err)
    }
}

我的数据结构

struct UserData {

let uid: String
let username: String

init(dictionary: [String: Any]) {
    self.uid = dictionary["id"] as? String ?? ""
    self.username = dictionary["username"] as? String ?? ""
    }
}

Answer 1

observeSingleEvent可能只是在获取第一个条目。查看Firebase数据库文档here，您会发现他们使用observe获取列表。尝试像这样遍历所有孩子：

ref.observe(.value) { snapshot in
    for child in snapshot.children.allObjects as! [DataSnapshot] {
        print(child.value)
        let dict = child.value as? [String : AnyObject] ?? [:]
        print(dict["title"])
    }
}

因此，您要返回数组的任何地方都可以使用上述observe方法，而您只希望单个数据输入的任何地方都可以使用observeSingleEvent。>