Question

我正在尝试在Firebase数据库中写入一些数据，但是我得到了错误的运行过程。有人可以帮我吗？非常感谢！！

JSON树结构如下：

{ 
    "cars": {

        "auto id": [

            "parts": "wheel"
             ...
    .
    .
    .



@objc func buttonTapped(){

    print("before running")
        var ref = Database.database().reference(withPath: "cars").queryOrdered(byChild: "parts").queryEqual(toValue: "wheel")
            ref.observeSingleEvent(of: .childAdded, with: { (snapshot) in
            autoId = snapshot.key
            print("running")
        }) { (error) in
            print(error.localizedDescription)
        }
print("after running")
let newPlanetRef = Database.database().reference().child("company").childByAutoId()
                    newPlanetRef.updateChildValues(autoId)
}

我希望运行的过程是

“正在运行”->“正在运行”->“正在运行”

但是实际过程是

“正在运行”->“正在运行”->“正在运行” 除非我将更新功能放在闭包内，否则数据无法更新到数据库

Answer 1

这是一个异步过程。

您应该这样使用：

'{"en":"Goodbye","fr":"Bonjour"}'

但是我认为这样使用：

为您的参考键创建私有枚举：

var newPlanetRef: String? //It should be your reference type

var ref = Database.database().reference(withPath: "cars").queryOrdered(byChild: "parts").queryEqual(toValue: "wheel")
        ref.observeSingleEvent(of: .childAdded, with: { (snapshot) in
        autoId = snapshot.key
        newPlanetRef = Database.database().reference().child("company").childByAutoId()
        newPlanetRef.updateChildValues(autoId)
        print("running")
    }) { (error) in
        print(error.localizedDescription)
    }

创建数据库引用的全局变量：

private enum ReferenceKeys {
    static let carsKey = "cars"
}

像这样使用您的函数：

var database = Database.database()
var databaseReference = database.reference()
var carReference = database.reference(withPath: ReferencesKeys.carsKey)

奖金：

您可以使用dispatchGroup（或信号量）来等待快照值以继续：

DispatchGroup

var newPlanetRef: String?

var reference = carReference.queryOrdered(byChild: "parts").queryEqual(toValue: "wheel")

reference.observeSingleEvent(of: .childAdded, with: { [weak self] snapshot in

    self?.autoId = snapshot.key
    newPlanetRef = databaseReference.child("company").childByAutoId()
    newPlanetRef.updateChildValues(autoId)

    print("running")
}) { error in 

    print(error.localizedDescription)
}

DispatchSemaphore

@objc func buttonTapped(){

    let dispatchGroup = DispatchGroup()

    print("before running")
    var ref = Database.database().reference(withPath: "cars").queryOrdered(byChild: "parts").queryEqual(toValue: "wheel")

    dispatchGroup.enter()
    ref.observeSingleEvent(of: .childAdded, with: { [weak self]snapshot in
            self?.autoId = snapshot.key

            dispatchGroup.leave()
            print("running")
    }) { (error) in
            print(error.localizedDescription)
    }
    print("after running")
    let newPlanetRef = Database.database().reference().child("company").childByAutoId()
    newPlanetRef.updateChildValues(autoId)
}

完成

@objc func buttonTapped(){

    let dispatchSemaphore = DispatchSemaphore(value: 1)

    print("before running")
    var ref = Database.database().reference(withPath: "cars").queryOrdered(byChild: "parts").queryEqual(toValue: "wheel")

    ref.observeSingleEvent(of: .childAdded, with: { [weak self]snapshot in
            self?.autoId = snapshot.key
            semaphore.signal()

            print("running")
    }) { (error) in
            print(error.localizedDescription)
    }

    semaphore.wait()

    print("after running")
    let newPlanetRef = Database.database().reference().child("company").childByAutoId()
    newPlanetRef.updateChildValues(autoId)
}

从Firebase数据库查询数据时的奇怪行为

1 个答案: