Empty Core Data Table - swift

Question

I would like to remove all data from a selected Core Data Entity. I'm using the below code but getting the following error:
Unresolved identifier managedObjectContext
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "UserAccountTbl")
let batchDeleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
do {
try managedObjectContext.executeRequest(batchDeleteRequest)
} catch {
// Error Handling
}

Answer 1

First of all – as already mentioned in the other answers – you have to get the NSManagedObjectContext from AppDelegate
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let managedObjectContext = appDelegate.persistentContainer.viewContext
Force unwrapping is perfectly fine, the application wouldn't even launch if AppDelegate was missing.
But there is a caveat:
If you call execute on the managed object context you have to merge the changes into the context because the execute operation doesn't modify the content of the context.
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "UserAccountTbl")
let batchDeleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
batchDeleteRequest.resultType = .resultTypeObjectIDs
do {
let result = try managedObjectContext.execute(batchDeleteRequest) as! NSBatchDeleteResult
let changes = [NSDeletedObjectsKey : result.result as! [NSManagedObjectID]]
NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes, into: [managedObjectContext])
} catch {
print(error)
}
However you can avoid the merge step if you call execute on the persistent store coordinator
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "UserAccountTbl")
let batchDeleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
do {
let persistentStoreCoordinator = managedObjectContext.persistentStoreCoordinator!
try persistentStoreCoordinator.execute(batchDeleteRequest, with: managedObjectContext)
} catch {
print(error)
}

Answer 2

Seems like you haven't declared your managedObjectCotext and trying to access it. Try this:
let managedObjectContext = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "UserAccountTbl")
let batchDeleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
do {
try managedObjectContext.executeRequest(batchDeleteRequest)
} catch {
// Error Handling
}

Answer 3

As from your error, you have not declare context from container which is in appDelegate. You can try with following code:
guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
//We need to create a context from this container
let managedObjectContext = appDelegate.persistentContainer.viewContext
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "UserAccountTbl")
let batchDeleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
do {
try managedObjectContext.executeRequest(batchDeleteRequest)
} catch {
// Error Handling
}