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iOS Introduction to Core Data with Swift 2 Fetching Data Using Fetch Requests Performing a Fetch Request

luke jones
luke jones
8,915 Points
Posted by luke jones
luke jones
8,915 Points

NSFetchRequest Swift 3 Syntax

Trying to create a fetch request with swift 3 (Swift 2 show in video):

 lazy var fetchRequest: NSFetchRequest<Item> = { 
    let request = NSFetchRequest<Item>(entityName: Item.identifier)
    let sortDescriptor = NSSortDescriptor(key: "text", ascending: true)
    request.sortDescriptors = [sortDescriptor]
    return request
}()

Although can't seem to get it to work. In view did load:

    do {
        items = try managedObjectContext.execute(fetchRequest) as! Item
    } catch let error as NSError {
        print("Error fetching Item objects: \(error.localizedDescription), \(error.userInfo)")
    }

which displays a warning stating that cast from 'NSPersistentStoreResult' to unrelated type '[Item]' always fails therefore crashing the app.

1 Answer

Dennis Parussini
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Dennis Parussini
Treehouse Project Reviewer
Dennis Parussini
.a{fill-rule:evenodd;}techdegree seal-36
Dennis Parussini
Treehouse Project Reviewer

There's a slightly different method used in Swift 3. You need to use the fetch() method to perform the fetching now.

items = try managedObjectContext.fetch(fetchRequest)

The rest works as usual.

Actually there's a completely new way of doing things in Swift 3. Instead of writing all this

lazy var fetchRequest: NSFetchRequest<Item> = {
        let request = NSFetchRequest<Item>(entityName: Item.identifier)
        let sortDescriptor = NSSortDescriptor(key: "text", ascending: true)
        request.sortDescriptors = [sortDescriptor]
        return request
    }()

you can now create an NSFetchRequest with

let request: NSFetchRequest<Item> = Item.fetchRequest()
Alexa Noverra
Alexa Noverra
566 Points

Well, you are right but is good to know how to make the request manually.