如何在 Swift 5 中强制更新 CoreData 代码文件（属性扩展）？

Question

i am a bit confused with CoreData. In my xcdatamodeld I am able to create new properties and change some things about them, like whether they are optional or not .

For example, I created a property for my entity and called it descrip , the type is a String and I checked the Optional Field .

At some other point I try to create a new Object of this Entity and safe it to CoreData:

let newEntity = Entity(context: context)
newEntity.name = name
newEntity.descrip = descrip // descrip is an optional String
newEntity.filename = filename

I get the following error message: Value of optional type 'String?' must be unwrapped to a value of type 'String' Value of optional type 'String?' must be unwrapped to a value of type 'String'

Then, I tried to create the NSManagedObjectSubclasses for my Entity. I discovered, that while all properties have been added and the type of all is set correctly, the? indicating the Optionality of the property was messed up completely.

import Foundation
import CoreData


extension Entity {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Entity> {
        return NSFetchRequest<Entity>(entityName: "Entity")
    }

    @NSManaged public var name: String? // Should not be optional and was set so in xcdatamodeld
    @NSManaged public var descrip: String // Should be optional and set to optional in xcdatamodeld
    @NSManaged public var filename: String
}

Is there any way to force update this code file? Or how can I use optional strings to fill out my new Entity's optional values?

Answer 1

The error in that assignment is not a Core Data problem, it's pure Swift. You've declared descrip as String , yet you are trying to assign a String? value. That's not legal in Swift-- you must unwrap an optional before assigning it to a non-optional. It would be the same if you weren't using Core Data. For example this would produce the same error:

let foo: String? = "hello"
let bar: String = foo

The differences between the data model and the generated code happen because Swift optionals and Core Data optionals are completely different things. Core Data only cares if something is optional when you save changes. Swift cares about whether something is optional all the time. It's different because Core Data was around for a long time before Swift existed, so it doesn't always match up with what Swift expects.