Question

当我的应用程序首次启动时，我会做一些首次设置配置，它使用CoreData API为我的SQLLite数据库提供来自JSON文档的数据。

我首先从核心数据堆栈获取对托管对象上下文的引用，然后调用执行JSON配置的方法。然后我打电话给：

....(JSON conversion)....

context.perform {
 _ = Exercise.insert(into: context, name: exerciseName, category: categoryNumber, equipment: equipment, skill: "", primaryMuscle: primaryMuscle, otherMuscles: otherMuscles, info: exerciseDescription, image1: exerciseImage1, image2: exerciseImage2)
   }

在每次迭代时，我遍历JSON对象，因此它会持久保存每个对象。

插入对象的方法是：

public static func insert(into context: NSManagedObjectContext, name: String, category: Int16, equipment: String?, skill: String?, primaryMuscle: String?, otherMuscles: String?, info: String?, image1: String?, image2: String?) -> Exercise {
    let exercise: Exercise = context.insertObject()
    exercise.name = name
    exercise.category = category
    exercise.info = info
    exercise.primaryMuscle = primaryMuscle
    exercise.otherMuscles = otherMuscles
    exercise.equipment = equipment
    exercise.skill = skill

    if image1 != nil {
        exercise.image1Path = image1
    }

    if image2 != nil {
        exercise.image2Path = image2
    }

    return exercise
}

然后我扩展了NSManagedObjectContext ...

extension NSManagedObjectContext {
public func insertObject<Object: NSManagedObject>() -> Object where Object: Managed {
    guard let obj = NSEntityDescription.insertNewObject(forEntityName: Object.entityName, into: self) as? Object else { fatalError("Wrong object type") }
    return obj
}
}

这是我对我＆＃34; Managed＆＃34;的声明。协议：

public protocol Managed: class, NSFetchRequestResult {
static var entityName: String {get}
....
   }

extension Managed where Self: NSManagedObject {
public static var entityName: String { return entity().name! }
 }

然后我试图从协议扩展中检索entityName时崩溃，我试图插入对象......

它给了我错误＆＃34;致命错误：在展开可选值时意外地发现了nil＆＃34;

我没有生成我的NSManagedObjectSublcasses，我自己创建了它们，但我确定我做得正确。我有一种感觉，虽然核心数据并没有拿起我的Model课程，因为＃34;练习＆＃34;当应用程序运行时。这就是实体名称没有返回的原因。所以这是我的模型类的代码：

import UIKit
import CoreData

public class Exercise: NSManagedObject {

@NSManaged public fileprivate(set) var category: Int16
@NSManaged public fileprivate(set) var image1Path: String?
@NSManaged public fileprivate(set) var image2Path: String?
@NSManaged public fileprivate(set) var equipment: String?
@NSManaged public fileprivate(set) var info: String?
@NSManaged public fileprivate(set) var skill: String?
@NSManaged public fileprivate(set) var primaryMuscle: String?
@NSManaged public fileprivate(set) var otherMuscles: String?

public static let normalizedNameKey = "name_normalized"

@NSManaged fileprivate var primitiveName: String

public var name: String {
    set {
        willChangeValue(forKey: #keyPath(Exercise.name))
        primitiveName = newValue
        updateNormalizedName(newValue)
        didChangeValue(forKey: #keyPath(Exercise.name))
    }
    get {
        willAccessValue(forKey: #keyPath(Exercise.name))
        let value = primitiveName
        didAccessValue(forKey: #keyPath(Exercise.name))
        return value
    }
}

fileprivate func updateNormalizedName(_ name: String) {
    setValue(name.normalizedForSearch, forKey: Exercise.normalizedNameKey)
}

public var exerciseImage1: UIImage? {
    guard let image = image1Path else {return nil}
    return UIImage(named: image)
}

public var exerciseImage2: UIImage? {
    guard let image = image2Path else {return nil}
    return UIImage(named: image)
}

 public static func insert(into context: NSManagedObjectContext, name: String, category: Int16, equipment: String?, skill: String?, primaryMuscle: String?, otherMuscles: String?, info: String?, image1: String?, image2: String?) -> Exercise {
    let exercise: Exercise = context.insertObject()
    exercise.name = name
    exercise.category = category
    exercise.info = info
    exercise.primaryMuscle = primaryMuscle
    exercise.otherMuscles = otherMuscles
    exercise.equipment = equipment
    exercise.skill = skill

    if image1 != nil {
        exercise.image1Path = image1
    }

    if image2 != nil {
        exercise.image2Path = image2
    }

    return exercise
}

}

  extension Exercise: Managed {

  public static var defaultSortDescriptors: [NSSortDescriptor] {
    return [NSSortDescriptor(key: #keyPath(name), ascending: false)]
  }

public static func defaultPredicate(muscleCategory: Int) -> NSPredicate 
 {
    return NSPredicate(format: "%K == %ld", 
 #keyPath(Exercise.category), muscleCategory)
}
}

这是数据模型编辑器中的实体：

任何想法可能会出错？感谢

Answer 1

我有完全相同的问题，使用完全相同的代码（Florian Kugler的核心数据手册）。

我添加新实体+关系后出现问题，创建新实体时，实体名称为nil 我通过删除实体并再次重新创建它来修复它。错误消失了。

Answer 2

也许这不是一个好主意，但现在可以避免崩溃......等待更好的解决方案。

斯普利特4：

extension NSObject {
    var className: String {
        return String(describing: type(of: self))
    }

    class var className: String {
        return String(describing: self)
    }
}

然后

static var entityName: String {
    return self.className //insead of `entity().name!`
}

Answer 3

我在Florian Kugler的核心数据书中也遇到了同样的问题。不幸的是，@ Kobe的回答没有帮助。我通过在核心数据模型的文件检查器中选择“类的模块”解决了该问题。

先前已将其设置为“无”。

Answer 4

莫因，

首先解开可选值。

    public static var entityName: String 
    { 
        if let _returnName = entity().name{
            return _returnName
        }else
        {
            return nil
        } 
   }
}

Optional Chaining

CoreData：

课程练习

当您更改dbModel并执行“Create NSManagedObject Sub ..”时，练习中的所有函数都将被覆盖。

使用类似 ExerciseExtension

的单独类

import UIKit
import CoreData

extension Exercise {
  func setName(name : String)
  {
    self.name = name
  }
  .....
}

Answer 5

在iOS 10.3+上使用Xcode 9.4.1的Swift 4.1 projet上，我遇到了类似的问题我试图做这样的事情：

    guard let description = Entity.entity(),
      throw Error.entityNotFound
    }
    *[some code]*
    context.perform {
    *[some code]*
    }

但是我的一些单元测试失败了，其他的则工作得很好。我的xcdatamodel和我的NSManagedObject子类都很好。最后，我通过获取perform闭包内的实体名称来使其工作：

    context.perform {
    guard let description = Entity.entity(),
      throw Error.entityNotFound
    }
    *[some code]*
    }

检索实体名称时崩溃了吗？

5 个答案: