CoreData NSPredicate

Question

我将一个旧项目从Swift 1转换为SWIFT4.2(在主要版本步骤中，都是成功构建的)，使用CoreData。

现在，当试图执行此代码时，编译器会在下面抛出错误：

let sortDescriptor = NSSortDescriptor(key: "dateModified", ascending: false)
let predicate = NSPredicate(format: "markAsDeleted == false")
if let itemInspections = item.inspections?.filtered(using: predicate).sortedArray(using: [sortDescriptor]) {
    label.text = "Items (\(itemInspections.count))"
}

错误：

2018-09-25 17:19:06.606722+0200 AppName538:144354 -_NSFaultingMutableSet filteredOrderedSetUsingPredicate:：未识别的选择器发送给实例0x17063afc0 2018-09-25 17:19:06.607861+0200 AppName538:144354 *由于不明异常'NSInvalidArgumentException'，原因：‘_NSFaultingMutableSet filteredOrderedSetUsingPredicate:：未识别的选择器发送到实例0x17063afc0’ *第一次抛出调用堆栈：(0x18f5d6fd8 0x1818e038538 0x18f5ddef4 0x18f5df5df4c 0x18f4d6d2c 0x100126ce0 0x10015fa10 0x10015fa10 0x10015fc18 0x195ff9268 0x19575f884 0x19575a4ac 0x1956fc158 0x1928ec274 0x1928e0de8 0x28e0ca8 0285c360 0x0x1956f6f17a0 18f4958a0 0x18f4958a0 0x18f492828 0x18f774 0fb4d2x74x11x1x1918c0c0 0 288c360 0x1956c0 0x1956f17a0 18f4958a0 0x18f5828 0x18f774) libc++abi.dylib:以NSException类型的未明确例外结束

任何指针都将不胜感激。

Answer 1

最后，我将检查类型更改为NSSet，并显式转换筛选(using：_) ->的结果，更改代码如下：

let sortDescriptor = NSSortDescriptor(key: "dateModified", ascending: false)
let predicate = NSPredicate(format: "markAsDeleted == false")        
if let itemInspections = NSSet(set: (item.inspections?.filtered(using: predicate))!).sortedArray(using: [sortDescriptor]) as? [Inspection] {
    inspectionsCountLabel.text = "Inspections (\(itemInspections.count))"
}

谢谢你的评论，他们为我指明了正确的方向！

Answer 2

强烈建议使用适当的谓词和排序描述符重新获取项，而不是手动进行。

代码假定有一个NSManagedObject子类Inspection具有关系item，由item表示的实体具有唯一的属性name。

let sortDescriptor = NSSortDescriptor(key: "dateModified", ascending: false)
let predicate = NSPredicate(format: "item.name == %@ AND markAsDeleted == FALSE", item.name)
let fetchRequest : NSFetchRequest<Inspection> = Inspection.fetchRequest()
fetchRequest.predicate = predicate
fetchRequest.sortDescriptors = [sortDescriptor]
do {
    let itemInspections = try managedObjectContext.fetch(fetchRequest)
    label.text = "Items (\(itemInspections.count))"
} catch { print(error) }

如果您只需要过滤项的数量，则有一个更有效的API。

let sortDescriptor = NSSortDescriptor(key: "dateModified", ascending: false)
let predicate = NSPredicate(format: "item.name == %@ AND markAsDeleted == FALSE", item.name)
let fetchRequest : NSFetchRequest<Inspection> = Inspection.fetchRequest()
fetchRequest.predicate = predicate
fetchRequest.sortDescriptors = [sortDescriptor]
do {
    let numberOfItemInspections = try managedObjectContext.count(for: fetchRequest)
    label.text = "Items (\(numberOfItemInspections))"
} catch { print(error) }

Answer 3

尝试避免实体属性的显式字符串，还可以用正确的格式表达式替换false：

let sortDescriptor = NSSortDescriptor(key: "\#keyPath(YourClassHere.dateModified)", ascending: false)
let predicate = NSPredicate(format: "\#keyPath(YourClassHere.markAsDeleted) == @%", NSNummber(value: false))
if let itemInspections = item.inspections?.filtered(using: predicate).sortedArray(using: [sortDescriptor]) {
    label.text = "Items (\(itemInspections.count))"
}