我为demo project和demo video准备了一个问题。
我想知道如何正确使用transaction.edit。
当前，如果您看一下我的demo project，有一个名为updateCompany的函数，我在其中将员工添加到公司中：
func updateCompany(with company: Company, completion: @escaping (Result<Company, Error>) -> Void) {
CoreStore.perform(
asynchronous: { (transaction) -> Company in
let editCompany = transaction.edit(company)!
editCompany.name = company.name
if let unwrappedEmployees = company.employees {
for employee in unwrappedEmployees {
if let castedEmployee = employee as? Employee {
let editEmployee = transaction.edit(castedEmployee)!
editCompany.addToEmployees(editEmployee)
}
}
}
return editCompany
},
success: { (transactionCompany) in
guard let fetchedObject = CoreStore.fetchExisting(transactionCompany) else {
return
}
completion(.success(fetchedObject))
},
failure: { (error) in
completion(.failure(error))
})
，在这种情况下，所有记录都正确保存，一切正常。但是令我感到奇怪的是，transaction.edit函数描述说它“返回指定的NSManagedObject或CoreStoreObject的可编辑代理。”
因此，作为该功能的首次用户，您怀疑实际上是NSManagedObject的代理（在我的情况下，这是上面的company实例）与许多员工的关系已经存在。作为该函数的首次用户，您可以编写下一个代码：
func updateCompany(with company: Company, completion: @escaping (Result<Company, Error>) -> Void) {
CoreStore.perform(
asynchronous: { (transaction) -> Company in
let editCompany = transaction.edit(company)!
// take a look print(editCompany.employees)
// suspect all employees are there, but they are not!
return editCompany
},
success: { (transactionCompany) in
guard let fetchedObject = CoreStore.fetchExisting(transactionCompany) else {
return
}
// WHICH IS MORE STRANGE all added employees are returned here from successful transaction
completion(.success(fetchedObject))
},
failure: { (error) in
completion(.failure(error))
})
当您意识到发生了一件奇怪的事时，我们打开documentation并说：
请勿更新不是通过创建或获取的实例 交易。如果您已经有对该对象的引用，请使用 事务的edit（...）方法来获取可编辑的代理实例 该对象
正如您从演示项目中看到的那样，我更新了NSSet的{{1}}，它们是在employees外部获取的，但是我猜这是关于执行异步/同步{{ 1}}，用于更新transaction
请纠正我使用transaction的正确方法。