Deniss Deniss - 1 month ago 10
Swift Question

How to apply the type to a NSFetchRequest instance?

In Swift 2 the following code was working:

let request = NSFetchRequest(entityName: String)


but in Swift 3 it gives error:


Generic parameter "ResultType" could not be inferred


because
NSFetchRequest
is now a generic type. In their documents they wrote this:

let request: NSFetchRequest<Animal> = Animal.fetchRequest


so if my result class is for example
Level
how should I request correctly?

Because this not working:

let request: NSFetchRequest<Level> = Level.fetchRequest

Answer
let request: NSFetchRequest<NSFetchRequestResult> = Level.fetchRequest()

or

let request: NSFetchRequest<Level> = Level.fetchRequest()

depending which version you want.

You have to specify the generic type because otherwise the method call is ambiguous.

The first version is defined for NSManagedObject, the second version is generated automatically for every object using an extension, e.g:

extension Level {
    @nonobjc class func fetchRequest() -> NSFetchRequest<Level> {
        return NSFetchRequest<Level>(entityName: "Level");
    }

    @NSManaged var timeStamp: NSDate?
}

The whole point is to remove the usage of String constants.

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