Decodable CoreStoreObject subclass implementation #239

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adam · 2025-12-29T15:27:12+01:00

adam commented

2025-12-29 15:27:12 +01:00

Originally created by @eraydiler on GitHub (Oct 29, 2018).

Hello,

I'm trying to figure out how to implement a CoreStoreObject subclass that also needs to conform to Decodable protocol. What I came up with is the code below.

`
class TestObject: CoreStoreObject, Decodable {
let title = Value.Optional("title", initial: nil)

 private enum CodingKeys: String, CodingKey {
     case title = "title"
 }

 required init(from decoder: Decoder) throws {
     let values = try decoder.container(keyedBy: CodingKeys.self)

     title.value = try values.decodeIfPresent(String.self, forKey: .title)

     super.init(asMeta: ())
 }

 required init(asMeta: Void) {
     super.init(asMeta: ())
 }

 required init(rawObject: NSManagedObject) {
     super.init(asMeta: ())
 }

}
`

However I'm having error;
❗ [CoreStore: Assertion Failure] Value.swift:373 value
↪︎ Attempted to access values from a 'Test' meta object. Meta objects are only used for querying keyPaths and infering types.

I think issue is related to the init(asMeta:...), init(rawObject:...) methods' implementation.
What is the proper way to implement these methods?
Thanks.

Originally created by @eraydiler on GitHub (Oct 29, 2018). Hello, I'm trying to figure out how to implement a CoreStoreObject subclass that also needs to conform to Decodable protocol. What I came up with is the code below. ` class TestObject: CoreStoreObject, Decodable { let title = Value.Optional<String>("title", initial: nil) private enum CodingKeys: String, CodingKey { case title = "title" } required init(from decoder: Decoder) throws { let values = try decoder.container(keyedBy: CodingKeys.self) title.value = try values.decodeIfPresent(String.self, forKey: .title) super.init(asMeta: ()) } required init(asMeta: Void) { super.init(asMeta: ()) } required init(rawObject: NSManagedObject) { super.init(asMeta: ()) } } ` However I'm having error; ❗ [CoreStore: Assertion Failure] Value.swift:373 value ↪︎ Attempted to access values from a 'Test' meta object. Meta objects are only used for querying keyPaths and infering types. I think issue is related to the `init(asMeta:...), init(rawObject:...)` methods' implementation. What is the proper way to implement these methods? Thanks.

adam closed this issue

2025-12-29 15:27:12 +01:00

adam commented

2025-12-29 15:27:13 +01:00

@JohnEstropia commented on GitHub (Oct 30, 2018):

As mentioned somewhere in the discussion in mogenerator's prototype for Codable support, NSManagedObjects generally do not really play well with Encodable because the init(decoder:) needs to be implemented, while NSManagedObject's init(context:) needs an instance of the NSManagedObjectContext where the object will be added. (Basically you can call init(decoder:) many times without side effects, but init(context:) does)

You are hitting the same limitation with CoreStoreObject here, where it needs the context (via the NSManagedObject in init(rawObject:)).

You can borrow the techniques used in the mogenerator proposal above, but at that point I would recommend you to use ImportableUniqueObjects instead as they are much much more simple.

@JohnEstropia commented on GitHub (Oct 30, 2018): As mentioned somewhere in the discussion in [mogenerator's prototype for Codable support](https://github.com/rentzsch/mogenerator/issues/377), `NSManagedObject`s generally do not really play well with `Encodable` because the `init(decoder:)` needs to be implemented, while `NSManagedObject`'s `init(context:)` needs an instance of the `NSManagedObjectContext` where the object will be added. (Basically you can call `init(decoder:)` many times without side effects, but `init(context:)` does) You are hitting the same limitation with `CoreStoreObject` here, where it needs the context (via the `NSManagedObject` in `init(rawObject:)`). You can borrow the techniques used in the mogenerator proposal above, but at that point I would recommend you to use `ImportableUniqueObject`s instead as they are much much more simple.

adam commented

2025-12-29 15:27:14 +01:00

@eraydiler commented on GitHub (Oct 30, 2018):

I solved my issue by creating two different objects. They conform CoreStoreObject and Decodable seperately. Added additional methods to make required mapping between them. Thanks for the information.

@eraydiler commented on GitHub (Oct 30, 2018): I solved my issue by creating two different objects. They conform CoreStoreObject and Decodable seperately. Added additional methods to make required mapping between them. Thanks for the information.

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Reference: starred/CoreStore#239