Fetching entities in CoreData causing a crash

I have a model which looks like this and contains NSManagedObject properties, namely the blendsWith property which is a type of [Tag]:

blendsWith

[Tag]

extension Oil

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


@NSManaged public var blendsWith: [Tag]?
@NSManaged public var color: String?
@NSManaged public var commentsCount: Int64
@NSManaged public var id: Int64
@NSManaged public var imageURL: String?
@NSManaged public var latinName: String?
@NSManaged public var name: String?
@NSManaged public var properties: NSObject?
@NSManaged public var research: String?
@NSManaged public var resourceType: String?
@NSManaged public var viewsCount: Int64



public class Oil: NSManagedObject, Codable

enum CodingKeys: String, CodingKey
case resourceType = "resource_type"
case id, name
case imageURL = "image_url"
case color
case latinName = "latin_name"
case emotions
case safetyInformation = "safety_information"
case fact, research
case viewsCount = "views_count"
case commentsCount = "comments_count"
case blendsWith = "blends_with"
case foundInBlends = "found_in_blends"
case properties
case sourcingMethods = "sourcing_methods"
case usages


required convenience public init(from decoder: Decoder) throws
let context = CoreDataHelper.sharedInstance.persistentContainer.viewContext
guard let entity = NSEntityDescription.entity(forEntityName: "Oil", in: context) else fatalError()

self.init(entity: entity, insertInto: context)

let container = try decoder.container(keyedBy: CodingKeys.self)
self.resourceType = try! container.decodeIfPresent(String.self, forKey: .resourceType)!
self.id = try! container.decodeIfPresent(Int64.self, forKey: .id)!
self.name = try! container.decodeIfPresent(String.self, forKey: .name)!
self.imageURL = try! container.decodeIfPresent(String.self, forKey: .imageURL)!
self.color = try! container.decodeIfPresent(String.self, forKey: .color)!
self.viewsCount = try! container.decodeIfPresent(Int64.self, forKey: .viewsCount)!
self.viewsCount = try! container.decodeIfPresent(Int64.self, forKey: .viewsCount)!
self.commentsCount = try! container.decodeIfPresent(Int64.self, forKey: .commentsCount)!
self.latinName = try! container.decodeIfPresent(String.self, forKey: .latinName)!

if let blendsWith = try container.decodeIfPresent([Tag].self, forKey: CodingKeys.blendsWith)
self.blendsWith = blendsWith



public func encode(to encoder: Encoder) throws




Tag looks like this:

Tag

extension Tag

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


@NSManaged public var id: Int64
@NSManaged public var name: String?
@NSManaged public var resourceType: String?
@NSManaged public var tagType: String?
@NSManaged public var viewsCount: Int64



public class Tag: NSManagedObject, Codable

enum CodingKeys: String, CodingKey
case resourceType = "resource_type"
case id, name
case viewsCount = "views_count"
case tagType = "tag_type"


required convenience public init(from decoder: Decoder) throws
let context = CoreDataHelper.sharedInstance.persistentContainer.viewContext
guard let entity = NSEntityDescription.entity(forEntityName: "Tag", in: context) else fatalError()

self.init(entity: entity, insertInto: context)

let container = try decoder.container(keyedBy: CodingKeys.self)

self.resourceType = try! container.decodeIfPresent(String.self, forKey: .resourceType)!
self.id = try! container.decodeIfPresent(Int64.self, forKey: .id)!
self.name = try! container.decodeIfPresent(String.self, forKey: .name)!
if let viewsCount = try container.decodeIfPresent(Int64.self, forKey: .viewsCount)
self.viewsCount = viewsCount
else
self.viewsCount = 0

if let tagType = try container.decodeIfPresent(String.self, forKey: .tagType)
self.tagType = tagType
else
self.tagType = "lol"



public func encode(to encoder: Encoder) throws




When I go to fetch the Oil data stored locally, I get this crash:

Oil

2018-08-29 20:31:30.602764+0100 EL[27994:14799374] -[EL.Tag initWithCoder:]: unrecognized selector sent to instance 0x60c000679980
2018-08-29 20:31:30.603905+0100 EL[27994:14799374] [error] error: exception handling request: <NSSQLFetchRequestContext: 0x608000181ee0> , -[EL.Tag initWithCoder:]: unrecognized selector sent to instance 0x60c000679980 with userInfo of (null)
CoreData: error: exception handling request: <NSSQLFetchRequestContext: 0x608000181ee0> , -[EL.Tag initWithCoder:]: unrecognized selector sent to instance 0x60c000679980 with userInfo of (null)
2018-08-29 20:31:30.612185+0100 EL[27994:14799374] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[EL initWithCoder:]: unrecognized selector sent to instance 0x60c000679980'


What could be causing this crash?

For reference, my fetching method looks like this:

func getItems<T : NSManagedObject>(predicate : NSPredicate? = nil) -> [T]
do
let reqest = T.fetchRequest()
reqest.predicate = predicate
if let items = try persistentContainer.viewContext.fetch(reqest) as? [T]
return items
else
return [T]()

catch let error as NSError
print("Could not fetch. (error), (error.userInfo)")
return [T]()




And works like this:

let arrat : [Oil] = CoreDataHelper.sharedInstance.getItems()


NSKeyedUnArchiver

NSKeyedUnArchiver

initWithCoder

Oil.blendswith

NSSet

NSOrderedSet

2 Answers
2

If you debug this code does it ever step into the Tag init function? It appears the compiler is not seeing your Tag.init function which is most likely due to your Data Model for the Oil object not correctly setting the class type of the blendsWith property.

init

blendsWith

Check your data model for Oil and make sure that blendsWith is set to the correct type of Tag.

blendsWith

EDIT:
For Core Data to pick up your class setting you might need to add the objc flag before your class definition:

objc

@objc(Tag)
public class Tag ...


init

objc

A Transformable is usually coded by CoreData to Data (stored just as that), and coding an NSManagedObject may do things you do not expect. Decoding it could make things „more“ unexpected. (Coding done by NSKeyedArchiver and NSKeyedUnarchiver automatically on assignment/use.)

Transformable

Data

NSManagedObject

NSKeyedArchiver

NSKeyedUnarchiver

If you want to use Transformable then making it an NSManagedObject is pointless due to the argument above. (I at least have no experience with it, and have not heard what use it would have.)

Transformable

NSManagedObject

So its usually Transformable OR CoreData-relationships(with NSManagedObjects) to model one relationship in CoreData, but not both to model a single one.

Transformable

CoreData-relationships

NSManagedObject

Required, but never shown

Required, but never shown

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