Showing a UIAlertController when there is a NSConstraintConflict

I'm inserting data into my CoreData stack (which has only one entity with a few attributes). In Xcode, I've set the attribute "patientID" to be a unique constraint.
When attempting to add a new entry, this does as expected and throws an error in Xcode's console (NSConstraintConflict). However, in-app nothing is shown.

NSConstraintConflict

How would I go about adding a UIAlertController to state that this is a duplicate entry?

My current function for saving to CoreData is as follows:

func save(newID: String, newDOB: String, newAge: String, newGender: String, newHeight: String, newWeight: String, newRace: String, newADLS: String)

guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else
return


// 1
let managedContext = appDelegate.persistentContainer.viewContext

// 2
let entity = NSEntityDescription.entity(forEntityName: "Patient", in: managedContext)!

let person = NSManagedObject(entity: entity, insertInto: managedContext)

// 3
person.setValue(newID, forKeyPath: "patientID")
person.setValue(newDOB, forKey: "dob")
person.setValue(newAge, forKey: "age")
person.setValue(newGender, forKey: "gender")
person.setValue(newHeight, forKey: "height")
person.setValue(newWeight, forKey: "weight")
person.setValue(newRace, forKey: "race")
person.setValue(newADLS, forKey: "adls")

// 4
do
try managedContext.save()
dismiss(animated: true, completion: nil)

//No need for this - this occurs appends during viewWillAppear
//ids.append(person)

catch let error as NSError
print("Could not save. (error), (error.userInfo)")





1 Answer
1

You can fetch all records before every insert and verify that the new patientID doesn't exist before the insert and if exists show the alert

after you fetch the array

if fetchedArray.map$0.patientID.contains(newID)
// show alert here as id exists
return

// proceed in saving the new record


NSFetchRequest

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