How to run a generic method on a core data entity on Swift, the smarter way

Question

I have a lot of core data entities, they all have this method:

class func count(_ context:NSManagedObjectContext) -> Int

Suppose the entities are called: Car, Bus, Plane, etc.

What I would like to do is this, as I would normally.

let carCount = Car.count(coreDataContext)

of

 let busCount = Bus.count(coreDataContext)

but, all I have is the entity name, as described previously

How do I run that method from an entity just by the name of that entity?

Answer 1

Create a protocol with associated type

protocol Fetchable
{
    associatedtype FetchableType: NSManagedObject = Self
    static var entityName : String { get }
    static func count(_ context: NSManagedObjectContext) throws -> Int
}

and a protocol extension

extension Fetchable where Self : NSManagedObject
{
    
    static var entityName : String { return String(describing:self) }

    static func count(_ context: NSManagedObjectContext) throws -> Int
    {
        let request = NSFetchRequest<FetchableType>(entityName: entityName)        
        return try context.count(for: request)
    }
}

Adopt Fetchable in the NSManagedObject subclasses