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swift - 从 firebase 数据库查询数据时的奇怪行为

转载 作者:行者123 更新时间:2023-11-28 13:34:10 28 4
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我试图在 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)
}

我期望运行的进程是

"before running"->"running"->"after running"

但实际过程是

"before running"->"after running"->"running" And the data cannot be updated to database unless I put the update function inside the closure

最佳答案

这是一个异步过程。

你应该这样使用:

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)
}

但我认为这样使用:

  • 为您的引用 key 创建私有(private)枚举:

    private enum ReferenceKeys {
    static let carsKey = "cars"
    }
  • 创建数据库引用的全局变量:

    var database = Database.database()
    var databaseReference = database.reference()
    var carReference = database.reference(withPath: ReferencesKeys.carsKey)
  • 像这样使用您的函数:

    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)
    }

奖励:

您可以使用 dispatchGroup(或信号量)等待快照值以进行:

调度组

@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)
}

调度信号量

@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)
}

完成

@objc func buttonTapped(){

getData { [weak self] snapshotKey in
self?.autoId = snapshot.key
let newPlanetRef = Database.database().reference().child("company").childByAutoId()
newPlanetRef.updateChildValues(self?.autoId)
}
}

/// completion type -(String?)- must be a snapshot.key's type
func getData(_ completion: @escaping (String?) -> Void) {

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

ref.observeSingleEvent(of: .childAdded, with: { snapshot in
completion?(snapshot.key)

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

print("after running")

}

关于swift - 从 firebase 数据库查询数据时的奇怪行为,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/56898986/

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