Deleting all data in a Core Data entity in Swift 3

Question

Is there a way to do a batch delete of all data stored in all of the entities in core data?

I read somewhere that in iOS 9 or 10 that apple introduced a way to do batch deletes, but I can't seem to find any good information on it.

Ultimately, I just need a function that goes through an entity, and deletes all of the data in it. Seems like it should be simple enough, but documentation/tutorials for it have proven exceedingly difficult to find.

Any thoughts?

Edit

I added the following code into an IBAction attached to a button:

@IBAction func clearAllData(_ sender: AnyObject) {
    let fetch = NSFetchRequest<NSFetchRequestResult>(entityName: "PLProjects")
    let request = NSBatchDeleteRequest(fetchRequest: fetch)

    //get the data from core data
    getPLData()

    //reload the table view
    tableView.reloadData()
}

This does not seem to work however. If I close down the project and reopen it, the data is still there. I am assuming this is also why the table view doesn't update, because the data is not actually being deleted.

Answer 1

You're thinking of NSBatchDeleteRequest, which was added in iOS 9. Create one like this:

let fetch = NSFetchRequest<NSFetchRequestResult>(entityName: "Employee")
let request = NSBatchDeleteRequest(fetchRequest: fetch)

You can also add a predicate if you only wanted to delete instances that match the predicate. To run the request:

let result = try managedObjectContext.executeRequest(request)

Note that batch requests don't update any of your current app state. If you have managed objects in memory that would be affected by the delete, you need to stop using them immediately.

Answer 2

To flesh out Tom's reply, this is what I added to have a complete routine:

func deleteAllRecords() {
    let delegate = UIApplication.shared.delegate as! AppDelegate
    let context = delegate.persistentContainer.viewContext

    let deleteFetch = NSFetchRequest<NSFetchRequestResult>(entityName: "CurrentCourse")
    let deleteRequest = NSBatchDeleteRequest(fetchRequest: deleteFetch)

    do {
        try context.execute(deleteRequest)
        try context.save()
    } catch {
        print ("There was an error")
    }
}

Answer 3

Declare the Method for getting the Context in your CoreDataManager Class

     class func getContext() -> NSManagedObjectContext {
            guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
                return NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
            }
            if #available(iOS 10.0, *) {
                return appDelegate.persistentContainer.viewContext
            } else {
                return appDelegate.managedObjectContext
            }
        }

Call the above method from your NSManagedObject subClass:

    class func deleteAllRecords() {
            //getting context from your Core Data Manager Class
            let managedContext = CoreDataManager.getContext()
            let deleteFetch = NSFetchRequest<NSFetchRequestResult>(entityName: "Your entity name")
            let deleteRequest = NSBatchDeleteRequest(fetchRequest: deleteFetch)
            do {
                try managedContext.execute(deleteRequest)
                try managedContext.save()
            } catch {
                print ("There is an error in deleting records")
            }
    }