Unable to find specific subclass of NSManagedObject

Question

I'm working on developing an app with Core Data. When I created an instance using:

let entity = NSEntityDescription.entityForName("User", inManagedObjectContext: appDelegate.managedObjectContext)
let user = User(entity: entity, insertIntoManagedObjectContext: appDelegate.managedObjectContext)

I got a warning in log:

CoreData: warning: Unable to load class named 'User' for entity 'User'.  Class not found, using default NSManagedObject instead.

How could I fix it?

And another question, how can I define an instance method in NSManagedObject subclass?

Edit:

I have specified class of the entity as in the following screenshot:

enter image description here

Have you prefixed the entities class name with the module name, as documented in [Implementing Core Data Managed Object Subclasses](https://developer.apple.com/library/prerelease/mac/documentation/Swift/Conceptual/BuildingCocoaApps/WritingSwiftClassesWithObjective-CBehavior.html) ? — Martin R, Aug 01 '14 at 09:04
The class should be " YourAppName.User", see the documentation (link in my previous comment). — Martin R, Aug 01 '14 at 09:16
The best thing is to delete those classes and re create it. This worked for me — Abhishek, Oct 18 '15 at 12:14

score 221 · Accepted Answer · edited May 23 '17 at 12:18

221

Update for Xcode 7 (final): Prepending the module name to the class (as in Xcode 6 and early beta releases of Xcode 7) is no longer necessary. The Apple documentation Implementing Core Data Managed Object Subclasses has been updated accordingly.

The Data Model inspector has now two fields "Class" and "Module" for an entity:

When you create a Swift managed object subclass for the entity, the "Module" field is set to "Current Product Module", and with this setting creating instances works both in the main application and in unit tests. The managed object subclass must not be marked with @objc(classname) (this was observed in https://stackoverflow.com/a/31288029/1187415).

Alternatively, you can empty the "Module" field (it will show "None") and mark the managed object subclasses with @objc(classname) (this was observed in https://stackoverflow.com/a/31287260/1187415).

Remark: This answer was originally written for Xcode 6. There were some changes in the various Xcode 7 beta releases with respect to this problem. Since it is an accepted answer with many upvotes and links to it, I have tried to summarize the situation for the current Xcode 7 final version.

I did both my own "research" and read all the answers to both this question and the similar question CoreData: warning: Unable to load class named. So attribution goes to all of them, even if I don't list them specifically!

Previous answer for Xcode 6:

As documented in Implementing Core Data Managed Object Subclasses, you have to prefix the entities class name in the Class field in the model entity inspector with the name of your module, for example "MyFirstSwiftApp.User".

edited May 23 '17 at 12:18

Community

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answered Aug 01 '14 at 09:22

Martin R

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This one is working for me. Question: What if the core data is included in a framework, how to prefix the ManagedObject subclass name since there is no actual app yet? – Allan Macatingrao Sep 17 '14 at 10:07
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@Allan: You could try the `@objc(ClassName)` method suggested in Christer's answer. – Martin R Sep 17 '14 at 10:48
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It works, but once I've set the class name to "APPNAME.User" in the entity inspector, I am unable to regenerate model classes: Xcode seems to be confused by the prefix, and it generates a file/class with the name APPNAME. Am I missing something? – Pascal Bourque Sep 26 '14 at 15:26
Could you show how generated swift file looks like if its parent entity is NSManagedObjet and if is other custom Entity? I got some strange file content and compile time errors. – János Oct 22 '14 at 04:12
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What if you get this error in Objective-C when using core data in a static library? – George Taskos Dec 14 '14 at 00:53
@GeorgeTaskos: That looks like a different problem and seems already to be solved: http://stackoverflow.com/questions/27465485/coredata-warning-unable-to-load-class-named-weereadings-for-entity-readings. – Martin R Dec 14 '14 at 10:44
@Martin R yes, posted the comment before I add my own question to stackoverflow. – George Taskos Dec 14 '14 at 16:53
I have hyphens in my project name, I replaced them with underscores in the class name, it works. – Crazyrems Jan 23 '15 at 07:16
How can that work if you have two targets? your app and test? – Rodrigo Ruiz Mar 10 '15 at 06:31
@RodrigoRuiz: For that case the solutions from Christer's or Ludovic's answer might be better suited for you. – Martin R Mar 10 '15 at 07:47
It worked with the module prefix, I just would like to comment that the link is broken – Hola Soy Edu Feliz Navidad Mar 11 '15 at 10:38
@HolaSoyEduFelizNavidad: Thanks for noticing, I have updated the link. – Martin R Mar 11 '15 at 10:44
@MartinR, the automatically generated `@objc(ClassName)` now needs to be removed. – Suragch Aug 12 '15 at 07:19
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@Suragch: I have now finally update the answer, I do hope that everything is correct now. – Martin R Sep 20 '15 at 09:03
this worked for me: "Alternatively, you can empty the "Module" field (it will show "None") and mark the managed object subclasses with @objc(classname) (this was observed in ..." – spnkr Apr 27 '19 at 06:12

score 62 · Answer 2 · edited May 12 '15 at 12:08

62

Just as a side-note. i had the same issue. And all i had to do was add @objc(ClassName) in my class file.

Example:

@objc(Person)
class Person { }

And that solved my issue.

edited May 12 '15 at 12:08

Gurpartap Singh

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answered Aug 31 '14 at 12:01

Christer

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You defined typealias (.Person -> Person) in Objective-C in that way, so it works. – MsrButterfly Sep 03 '14 at 22:40
Seems like Apple forgot to fully convert it to the swift .. dont know why but this fixed it for me pretty gently – Jiří Zahálka Nov 30 '14 at 00:32
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This is particularly useful if you have a project with multiple targets, where each target shares the CoreData model. In these cases, it is not possible to prefix the class name with that of the target identifier as that renders the CD model useful to only one of the targets. – djbp Dec 10 '14 at 14:40
@djbp And "why not?" I'd like to know. I like the concept of namespacing, but this made me want to throw my MacBook out the window (I have an app with an extension, and hit this problem when running the extension). There has to be a "right" way to do this with namespaces, I just can't figure it out. – S'pht'Kr Dec 17 '14 at 17:52
Yup this worked for me when working with shared data models in a workspace – naz Mar 04 '15 at 04:14
This is the way to do it until they fix the subclass file naming bug in XCode – William T. Mar 17 '15 at 04:12
@S'pht'Kr And here we are, four months later with no solution. Unless anyone has a pleasing update? – Dandy Apr 10 '15 at 00:24
This answer is no longer true. – Suragch Aug 12 '15 at 07:20

score 31 · Answer 3 · answered Aug 05 '14 at 18:34

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The accepted answer to this question helped me resolve the same issue but I had a caveat that I thought would be helpful to others. If your project (module) name has a space in it you must replace the space with an underscore. For example:

Entity: MyEntity Class: My_App_Name.MyClass

answered Aug 05 '14 at 18:34

Mannix

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Exactly that I was looking for! Cheers! – manosim Dec 14 '14 at 18:06
When we set the class name with AppName.ClassName, Xcode 9 its remove the dot and create a class without a dot. So this is no longer in Xcode 9.*. – yo2bh Apr 24 '18 at 14:52

score 17 · Answer 4 · answered Jul 08 '15 at 08:25

17

Remember to remove your module:

enter image description here

answered Jul 08 '15 at 08:25

Bartłomiej Semańczyk

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This fixed my issue. – Jason Huh Jan 04 '16 at 14:00

score 9 · Answer 5 · answered Nov 07 '14 at 07:57

Depending if you are running as App vs Tests the issue can be that the app is looking for <appName>.<entityName> and when it's running as test it's looking as <appName>Tests.<entityName>. The solution I use at this time (Xcode 6.1) is to NOT fill the Class field in the CoreData UI, and to do it in code instead.

This code will detect if you are running as App vs Tests and use the right module name and update the managedObjectClassName.

lazy var managedObjectModel: NSManagedObjectModel = {
    // The managed object model for the application. This property is not optional...
    let modelURL = NSBundle.mainBundle().URLForResource("Streak", withExtension: "momd")!
    let managedObjectModel = NSManagedObjectModel(contentsOfURL: modelURL)!

    // Check if we are running as test or not
    let environment = NSProcessInfo.processInfo().environment as [String : AnyObject]
    let isTest = (environment["XCInjectBundle"] as? String)?.pathExtension == "xctest"

    // Create the module name
    let moduleName = (isTest) ? "StreakTests" : "Streak"

    // Create a new managed object model with updated entity class names
    var newEntities = [] as [NSEntityDescription]
    for (_, entity) in enumerate(managedObjectModel.entities) {
        let newEntity = entity.copy() as NSEntityDescription
        newEntity.managedObjectClassName = "\(moduleName).\(entity.name)"
        newEntities.append(newEntity)
    }
    let newManagedObjectModel = NSManagedObjectModel()
    newManagedObjectModel.entities = newEntities

    return newManagedObjectModel
}()

I tried your solution but I'm getting "fatal error: NSArray element failed to match the Swift Array Element type" when casting the NSManagedObject to its actual class. Actually not when casting itself, but when trying to go into a for loop. — Rodrigo Ruiz, Mar 11 '15 at 02:22
That example does not work if you have any sort of inheritance in your model. For every new entity you also need to iterate over subentites and update them with the new entities you created. — Anton, Mar 27 '15 at 23:06

score 8 · Answer 6 · answered Nov 18 '14 at 16:44

8

If you are using a hyphen in your project name like "My-App" then use an underscore instead of the hyphen like "My_App.MyManagedObject". In general, look at the name of the xcdatamodeld file and use the same prefix as in that name. I.e. "My_App_1.xcdatamodeld" requires the prefix "My_App_1"

answered Nov 18 '14 at 16:44

Rien

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wow. Thank you thank you thank you. I'd be interested in knowing where in the Apple docs that little nugget is :) – nh32rg Jan 10 '15 at 00:01

score 5 · Answer 7 · answered Jul 08 '15 at 09:00

5

This may help those experiencing the same problem. I was, with Swift 2 and Xcode 7 beta 2.

The solution in my case was to comment out @objc(EntityName) in EntityName.swift.

answered Jul 08 '15 at 09:00

enreas

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score 3 · Answer 8 · answered May 05 '15 at 19:50

I had the same warning, though my app appeared to run fine. The problem was that when running Editor > Create NSManagedObject Subclass on the last screen I used the default Group location, with no Targets displayed or checked, which saved the subclass in the top MyApp directory where MyApp.xcodeproj was located.
The warning went away when I instead changed the Group to be in the MyApp subfolder and checked the MyApp target.

score 2 · Answer 9 · answered Dec 16 '14 at 03:09

The above answers were helpful. This quick sanity check may save you some time. Go into Project > Build Phases > Compile Sources and remove your xcdatamodeld and your model files with the "-" button, and then add them right back with the "+" button. Rebuild -- that may take care of it.

score 2 · Answer 10 · edited Aug 02 '20 at 23:54

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By the way be careful what you add as a prefix: My App is called "ABC-def" and Xcode has converted the "-" into a "_".

To be safe look into the finder, find your project files and see what it says for your data model (for example "ABC_def.xcdatamodeld") and use what is written there EXACTLY!!!

edited Aug 02 '20 at 23:54

Duck

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answered May 19 '15 at 00:50

Mike

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score 1 · Answer 11 · answered Jan 13 '15 at 00:53

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The above answers helped me to solve different issue connected with Objective-C (maybe it will help someone):

If you refactored entity names, don't forget to change "Class" in "Utilities Panel" as well.

answered Jan 13 '15 at 00:53

Nat

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score 0 · Answer 12 · answered Feb 02 '17 at 11:43

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The above answers helped me but this may help somebody. If like me you did them and are still having a problem, remember to simply 'clean your project'. For XCode8, Product > Clean. Then run again.

answered Feb 02 '17 at 11:43

Olaolu Akinsete

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score -1 · Answer 13 · edited Nov 05 '20 at 13:39

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In Xcode 7 Entity and Class names can be the same but Codegen should be Class Definition. In that case there will be no warning etc.

edited Nov 05 '20 at 13:39

koen

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answered Jul 20 '17 at 09:35

Dario Caric

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Unable to find specific subclass of NSManagedObject

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