CODEWITHSUNDEEP
ioscore-dataswift
William Proffitt
William Proffitt

Reputation: 668

How come I can cast to NSManagedObject but not to my entity's type?

I'm using the Swift boilerplate code for Core Data in a fresh project. My .xcdatamodeld file has a single entity defined (Task) with a single attribute (name).

I have a Task.swift file that looks like this:

import CoreData

class Task: NSManagedObject {
    @NSManaged var name: String
}

When I run this, it works:

var firstTask = NSEntityDescription.insertNewObjectForEntityForName("Task",
    inManagedObjectContext: managedObjectContext) as NSManagedObject

firstTask.setPrimitiveValue("File my TPS reports", forKey: "name")

var error: NSError?

managedObjectContext.save(&error)

I can even go into the SQLite database being used by the iOS simulator and confirm that the row was added.

However, when I run the exact same code as above but with as Task instead of as NSManagedObject, I get a crash with the error message Thread 1: EXC_BREAKPOINT (code=EXC_I386_BPT, subcode=0x0), associated with the var firstTask… line. If I continue execution, I get EXC_BAD_ACCESS and 0 misaligned_stack_error_ at the top of Thread 1 each time I advance it.

Why might this cast lead to all this?

Upvotes: 38

Views: 20376

Answers (9)

kamimi01
kamimi01

Reputation: 1

This blog helped me! I implemented this for unit test btw.

I still don't know why I had to do this though...

guard let entity = NSEntityDescription.entity(forEntityName: "Task", in: context) else {
    XCTFail("❌ Failed to create entity")
    return
}
let task = Task(entity: entity, insertInto: context)  // This is Task type.

https://developer.apple.com/documentation/coredata/nsentitydescription/1425111-entity

Env: Xcode 16.2

Upvotes: 0

Viktor Kucera
Viktor Kucera

Reputation: 6335

Xcode 7 + Swift 2

Person.swift

@objc(Person)
class Person: NSManagedObject {
}

Data model

enter image description here

Then simply call

let person = NSEntityDescription.insertNewObjectForEntityForName("Person", inManagedObjectContext: self.managedObjectContext) as! Person

Upvotes: 4

Anson Yao
Anson Yao

Reputation: 1584

An update for @Ben Gottlieb answer under XCode 7.1 and Swift 2.0

  1. add @objc to your class. See Owen Zhao's answer. The following is an example:
@objc
class ImageRecordMO: NSManagedObject{

  1. Open your .xcdatamodled file.

  2. Select your entity and click the data model inspector on the right panel.

  3. Enter the class name, see the figure below

  4. Select your module to be Current Product Module, see the figure below.

enter image description here

Upvotes: 5

polarware
polarware

Reputation: 2519

This is even frustrated if you tried all the above suggestions and non of them working for me!!

So this is what works for me.

1- Select your xcdatamodeld file

2- Make sure that all your entities has No Module in the "Data Model Inspector", if you see "Model: Current Product Module" ..clear it it so it looks like the attached image.

3- Delete your App to clear core data

4- If still not working, delete your entities and regenerate them.

enter image description here

Upvotes: 31

Nicolas Chaussin
Nicolas Chaussin

Reputation: 21

I had to add the @objc() and set the class in the coredata interface. In the CoreData right window, in the Entity area, there are Name and Class textbox. Class must not be MSManagedObject but instead your class. I created a simple working example!

Upvotes: 2

Julien Couvreur
Julien Couvreur

Reputation: 4963

I've run into this problem in the last few days and strangely the solution that worked for me was a variant of that suggested above.

I added the @objc declaration to the generated subclasses, but removed any namespace prefix in the class name in the object model (it had a default prefix of "PRODUCT_MODULE_NAME." after the subclasses were generated). That worked.

Upvotes: 1

Jovan Jovanovski
Jovan Jovanovski

Reputation: 743

I guess only changing the class field in the .xcdatamodel doesn't work anymore because I still got the following exception: fatal error: use of unimplemented initializer 'init(entity:insertIntoManagedObjectContext:)' for class

So, I entered this code in my custom class:

    init(entity: NSEntityDescription!,
    insertIntoManagedObjectContext context: NSManagedObjectContext!) {
        super.init(entity: entity, insertIntoManagedObjectContext: context)
}

Suddenly, it worked! The NSManagedObject is now down-castable to my custom class. I can't really understand why this is the solution, but it works :)

Upvotes: 7

Owen Zhao
Owen Zhao

Reputation: 3355

You need to modify your Task.swift file. Adding @objc(Task) like below

import CoreData

@objc(Task)
class Task: NSManagedObject {
    @NSManaged var name: String
}

I think this as a bug if your project does not contain any objective-c codes. However, you need to add that line until this fixed.

I learned it from here.

Youtube video at 11:45

Upvotes: 11

Ben Gottlieb
Ben Gottlieb

Reputation: 85522

Make sure your Class name field is actually Module.Task, where Module is the name of your app. CoreData classes in Swift are namespaced. Right now, your object is being pulled out of the context as an NSManagedObject, not as a Task, so the as-cast is failing.

Upvotes: 50

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