因此，我试图确保在删除用户时以特定顺序执行一组异步任务。
所以我想要发生的是：
- 检查用户是否在购买时添加了客人
- 如果用户没有客人或根本没有任何购买，则从函数返回并继续删除过程（要点 6）
- 如果用户有任何购买的客人，请删除每个客人
- 删除所有客人后，继续删除他们所做的每笔购买
- 删除所有购买后，继续将实际用户本身从 Firestore 中删除
- 2 秒后，我将用户从 firebase 身份验证中删除，以确保尝试删除具有空用户的文档时不会发生崩溃
- 然后我只是转到主菜单
所以我试图用我的函数中的这段代码来完成这个：
let deleteAction = UIAlertAction(title: "Delete", style: .destructive) { (deletion) in
let semaphore = DispatchSemaphore(value: 0)
self.deleteButton.isHidden = true
self.loadingToDelete.alpha = 1
self.loadingToDelete.startAnimating()
DispatchQueue.global(qos: .background).async {
self.db.collection("student_users/\(user.uid)/events_bought").getDocuments { (querySnapshot, error) in
guard error == nil else {
print("The docs couldn't be retrieved for deletion.")
return
}
guard querySnapshot?.isEmpty == false else {
print("The user being deleted has no events purchased.")
return
}
for document in querySnapshot!.documents {
let docID = document.documentID
self.db.collection("student_users/\(user.uid)/events_bought/\(docID)/guests").getDocuments { (querySnap, error) in
guard querySnap?.isEmpty == false else {
print("The user being deleted has no guests with his purchases.")
return
}
for doc in querySnap!.documents {
let guest = doc.documentID
self.db.document("student_users/\(user.uid)/events_bought/\(docID)/guests/\(guest)").delete { (error) in
guard error == nil else {
print("Error deleting guests while deleting user.")
return
}
print("Guests deleted while deleting user!")
semaphore.signal()
}
semaphore.wait()
}
}
}
}
self.db.collection("student_users/\(user.uid)/events_bought").getDocuments { (querySnapshot, error) in
guard error == nil else {
print("There was an error retrieving docs for user deletion.")
return
}
guard querySnapshot?.isEmpty == false else {
return
}
for document in querySnapshot!.documents {
let docID = document.documentID
self.db.document("student_users/\(user.uid)/events_bought/\(docID)").delete { (err) in
guard err == nil else {
print("There was an error deleting the the purchased events for the user being deleted.")
return
}
print("Purchases have been deleted for deleted user!")
semaphore.signal()
}
semaphore.wait()
}
}
self.db.document("student_users/\(user.uid)").delete(completion: { (error) in
guard error == nil else {
print("There was an error deleting the user document.")
return
}
print("User doc deleted!")
semaphore.signal()
})
semaphore.wait()
}
DispatchQueue.main.asyncAfter(deadline: .now()+1.5) {
user.delete(completion: { (error) in
guard error == nil else {
print("There was an error deleting user from the system.")
return
}
print("User Deleted.")
})
}
self.loadingToDelete.stopAnimating()
self.performSegue(withIdentifier: Constants.Segues.studentUserDeletedAccount, sender: self)
}
在过去的几个小时里，我一直在尝试将DispatchSemaphore()其实现到我的代码中，但它并没有达到我期望的效果。我会阅读网上的文章和示例，DispatchSemaphore()但就我特别想做的事情而言，场景与我的并不完全相同。
当点击触发此警报操作时，不会打印任何内容，并且最终会永远旋转，用户不会从 Firebase 身份验证中删除，并且 Firestore 数据库中仍有剩余数据，如下所示：
我只是想找出在上面的有序列表中对这些异步任务进行排序的最佳方法，并在数据库中没有剩余的用户删除。提前致谢。