How to use NSSet created from Core Data

Question

I have the following core data model:

where Person to Codes is a one-to-many relationship.

I have a function which returns a Person record and if the code person.codes returns an NSSet of all the codes associated with that Person. The issue that I am having is how to use the NSSet.

person.codes.allObjects.first returns this data:

<Codes: 0x60000213cb40> (entity: Codes; id: 0xb978dbf34ddb849 <x-coredata://A2B634E4-E136-48E1-B2C5-82B6B68FBE44/Codes/p1> ; data: {
    code = 4LQ;
    number = 1;
    whosAccount = "0xb978dbf34ddb869 <x-coredata://A2B634E4-E136-48E1-B2C5-82B6B68FBE44/Person/p1>";
})

I thought if I made person.codes.allObjects.first of type Codes, I would be able to access the code and number elements but I get an error: error: value of type 'Any?' has no member 'number'

Also, how can I search this data set for a particular code or number.

I appreciate that this is proabably a simple question but have searched and read the documentation to no avail. I suspect that may base knowledge is not sufficient.

Update

I have a CoreDataHandler class which contains the following code:

class CoreDataHandler: NSObject {
    //static let sharedInstance = CoreDataHandler()

    private static func getContext() -> NSManagedObjectContext {
        let appDelegate = NSApplication.shared.delegate as! AppDelegate

        return appDelegate.persistentContainer.viewContext
    }

    static func fetchPerson() -> [Person]? {
        let context = getContext()

        do {
            let persons: [Person] = try context.fetch(Person.fetchRequest())
            return persons
        } catch {
            return nil
        }
    }

I can fetch a person using:

let row = personTableView.selectedRow
let person = CoreDataHandler.fetchPerson()?[row]

Weswesa

All objects takes the NSSet and makes an array – Weswesa

map it into an array first, if you need an index-based collection. – Silden

Answer 1

Core Data supports widely native Swift types.

Declare codes as Set<Codes> in the Person class.

It's much more convenient than typeless NSSet.
You get a strong type and you can apply all native functions like filter, sort, etc. without type cast.

Fatshan

I realize that it is probably an obvious question but how do I actually declare codes in the Person class? – Weswesa

You have to create the NSManagedObject subclasses manually. In the model file in the Entity Inspector change the Codegen popup of all entities to Manual/None, then in Menu Editor > Create NSManagedObject Subclass create the classes and change the types. – Fatshan

I have done that and have a Person class which looks like this:public class Person: NSManagedObject { }. How do I declare codes in that class? – Weswesa

There are two files per entity. A +CoreDataClass file and a +CoreDataProperties file. The properties are declared in the +CoreDataProperties file. – Fatshan

In my Person+.. file, I have: @NSManaged public var codes: Set<Codes>?. Now in my viewController class, this code works: let codes = person?.codes; let filteredCodes = codes!.filter({ $0.number == 1 }); print("key for code1= \(filteredCodes)") and prints out: key for code1= [<Codes: 0x60000213d360> (entity: Codes; id: 0xe7b68aa93f25f785 <x-coredata://.........> ; data: { code = 4LQ; number = 1; whosAccount = "0xe7b68aa93f25f7a5 <x-coredata://.......>"; })]. But filteredCodes.code is not recognised. How do I get to just the code, 4LQ? – Weswesa

First of all declare a to-many relationship as non-optional (Set<Codes>). Uncheck Optional also in the model file for the relationship. The result of filter is an array (note the []), If you want to get one item use first (which returns an optional). – Fatshan

Changed to non-optional and unchecked Optional also but let filteredCodes = codes!.filter({ $0.number == 1 }) and let code = filteredCodes.first both print out the same info: key for code1= [<Codes: 0x60000213d360> (entity: Codes; id: 0xe7b68aa93f25f785 <x-coredata://A2B634E4-E136-48E1-B2C5-82B6B68FBE44/Codes/p1> ; data: { code = 4LQ; number = 1; whosAccount = "0xe7b68aa93f25f7a5 <x-coredata://A2B634E4-E136-48E1-B2C5-82B6B68FBE44/Person/p1>"; })] – Weswesa

No, let filteredCodes = codes!.first{ $0.number == 1 } – Fatshan

Got it. Thank you very much! – Weswesa

I wonder why the autodefined classes after creating an entity doesn't do so. It's the behaviour everyone would expect – Mader

@Mader I found this: mjtsai.com/blog/2021/03/31/… – Elfland

Answer 2

let codes = person.codes as! Set<Code>

Once that is done you can access the properties. Searching can be done by filtering for instance

let filteredCodes = codes.filter({ $0.code == "XYZ" })

will return all objects that has the code "XYZ". Or to get only one you can use

let code = codes.first(where: {$0.id == 1})

which will return the first object that has id = 1

A simple example getting all Person objects that has a given code

func findWithCode(_ code: String) -> [Person] {
    guard let persons = CoreDataHandler.fetchPerson() else {
        return []
    }

    var result = [Person]()
    for person in persons {
        let codes = person.codes as! Set<Code>
        if codes.contains(where: { $0.code == code }) {
            result.append(person)
        }
    }

    return persons
}

Albi

I get this error when I try and typecast the set as Codes: Cast from 'NSSet?' to unrelated type 'Codes' always fails` – Weswesa

Have you tried as a native type let codes: Set<Codes> = person.codes? – Albi

If I try let codes: Set<Codes> = person.codes, I get this error: Cannot convert value of type 'NSSet?' to specified type 'Set<Codes> – Weswesa

@Weswesa My answer is incorrect in the typecasting, I'll update – Albi

if I try let codes = person.codes as! [Codes], I get this error: Cast from 'NSSet?' to unrelated type '[Codes]' always fails – Weswesa

Ah, you are missing a question mark since your method returns [Persons]?, try to change it to let codes = person?.codes as! [Codes]. Or if let codes = person?.codes as! [Codes] {...} – Albi

I still get the error: Cast from 'NSSet?' to unrelated type '[Codes]' always fails – Weswesa

No, as I am not sure how to do that. My Person class looks like this:public class Person: NSManagedObject { } – Weswesa

@Weswesa I did setup my own version of your model and used that to improve my answer – Albi

this line let codes = person.codes as! Set<Codes> would not work for me. The only way I could get it to work was to make this declaration @NSManaged public var codes: Set<Codes>? in my Person class extension. I don't understand why cast the NSSet as Codes in my ViewController – Weswesa

Ok. Well I did create an Xcode project with the same entities as yours and the above code works for me so there is nothing more I can do now. I also tried changing the declaration of codes in the Person class to Set<Codes> and that also worked. Anyway I guess you have a working solution by now using the other answer so all is good – Albi

I do have a working solution but it frustrates that I don’t understand why it wasn’t work – Weswesa