How to set an entities attribute via relationship? - swift

Question

I have the following entities and relationship
I want to be able to set an exercise to have a nil result for its routine name relationship, if that makes sense? so that it can later be set as a routine name when the routine entity is formed.
My question is, how do you set this sort of attribute up? I am trying the following code but it causes a fatal crash:
userExercise.usersroutine?.name = nil
My logic being that i take the exercise and follow the relationship to the name property and set it to nil?
Thanks for any correction and clarification on my logic
EDIT: Added my existing exercise and routine save functions
func createExercise() {
guard let managedObjectContext = managedObjectContext else { return }
if let userExercise = userExercise {
userExercise.name = userExerciseName.text
userExercise.sets = Int64(userSetsCount)
userExercise.reps = Int64(userRepsCount)
userExercise.weight = Double(self.userExerciseWeight.text!)!
userExercise.id = UUID().uuidString
userExercise.routine = nil
}
do {
try managedObjectContext.save()
} catch {
fatalError("Failure to save context: \(error)")
}
}
Routine Creation:
func createRoutine() {
guard let managedObjectContext = managedObjectContext else { return }
let userRoutine = UserRoutine(context: managedObjectContext)
userRoutine.name = workoutNameTextfield.text
do {
try managedObjectContext.save()
} catch {
fatalError("Failure to save context: \(error)")
}
}
Current Fetch Request:
fileprivate lazy var fetchedResultsController: NSFetchedResultsController<UserExercise> = {
let fetchRequest: NSFetchRequest<UserExercise> = UserExercise.fetchRequest()
fetchRequest.sortDescriptors = [NSSortDescriptor(key: "id", ascending: true)]
let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.persistentContainer.viewContext, sectionNameKeyPath: nil, cacheName: nil)
fetchedResultsController.delegate = self
return fetchedResultsController

Answer 1

Please check the implementation below I'have created some exercises and routines. Also read comments in code, this will help you figure out how to go about it.
Function to add a new exercise
func createExercise(weight: Int16, respetitions: Int16, name: String, routine: Routine?)->Exercise? {
let context = getMainContext()
let exercise = NSEntityDescription.insertNewObject(forEntityName: "Exercise", into: context) as! Exercise
exercise.setValue(weight, forKey: "weight")
exercise.setValue(name, forKey: "name")
exercise.setValue(respetitions, forKey: "rep")
do {
try context.save()
return exercise
}
catch
{
fatalError("unable to Ssavve")
}
}
Function to add a new routine
func createRoutine(name: String, exercises:[Exercise]) {
let context = getMainContext()
let routine = NSEntityDescription.insertNewObject(forEntityName: "Routine", into: context) as! Routine
routine.name = name
//Iterate over Exercise objects & check if routine is nil.
//Here if routine is not nil it menas your exercise is already assigned to a routine.
//If routine is nil assign routine.addToRelationship(<#T##value: Exercise##Exercise#>) and Also assign routine to the execise.
do {
try context.save()
}
catch
{
fatalError("unable to Ssavve")
}
}
Function to get main NSManagedObjectContext on which we can perform core-data actions
func getMainContext() -> NSManagedObjectContext {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
return appDelegate.persistentContainer.viewContext
}
Below, First I create few exercises without any relationship to routines
"The routine doesnt exist when the exercises are created, it is created afterward and its name is set"
and then create routines by passing some exercises (You can refer to other answer on how to fetch exercises with routine as nil values)
func initializer() {
//I'm adding exercises first without routines
let ex1 = self.createExercise(weight: 10, respetitions: 4, name: "Exercise1", routine: nil)
let ex2 = self.createExercise(weight: 5, respetitions: 10, name: "Exercise2", routine: nil)
let ex3 = self.createExercise(weight: 20, respetitions: 2, name: "Exercise3", routine: nil)
let ex4 = self.createExercise(weight: 5, respetitions: 10, name: "Exercise2", routine: nil)
self.createRoutine(name: "Routine 1", exercises: [ex1!, ex2!]) //You can pass all the exercises or use fetch request to query exercises with routine as nil
self.createRoutine(name: "Routine 2", exercises: [ex3!, ex4!])
self.createRoutine(name: "Routine 3", exercises: [ex1!, ex2!]) //This routine shall not be adding any execises as they are already added to othe routines
}
Updating create routine Function to query results of UserExercise which has usersroutine as nil
func createRoutine() {
guard let managedObjectContext = managedObjectContext else { return }
let userRoutine = UserRoutine(context: managedObjectContext)
userRoutine.name = workoutNameTextfield.text
//Getting nil value User Exercises
let request: NSFetchRequest<UserExercise> = UserExercise.fetchRequest()
request.predicate = NSPredicate(format: "usersroutine == nil")
do {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let context = appDelegate.persistentContainer.viewContext
let queryResults = try context.fetch(request)
//I like to check the size of the returned results!
print ("num of results = \(queryResults.count)")
//You need to convert to NSManagedObject to use 'for' loops
for exercise in queryResults as [NSManagedObject] {
//get the Key Value pairs (although there may be a better way to do that...
print("Exercise NAME: \(exercise.value(forKey: "name"))")
}
} catch {
print("Error with request: \(error)")
}
do {
try managedObjectContext.save()
} catch {
fatalError("Failure to save context: \(error)")
}
}

Answer 2

It doesn't seem that you should need to use the name attribute at all. This attribute should be used for storing the actual name of the UserRoutine and not for anything relationship based.
The relationships between entities in Core Data don't rely on a particular attribute of an entity, but between the entities themselves.
"I want the routine builder to look at the exercises and import all the exercises with nil in the relationship into it"
So...
Create a fetch request to fetch all the entities of UserExercise that don't have a related UserRoutine (i.e. where userroutine is nil).
let orphanedExerciseFetchRequest = NSFetchRequest(entityName: "UserExercises")
orphanedExerciseFetchRequest.predicate = NSPredicate(format: "userroutine == nil)
Execute this fetch request to get an array of UserExercises (with no related routine)
let orphanedExercises = managedObjectContext.executeFetchRequest(orphanedExerciseFetchRequest())
"creating a routine with attributed exercises"
Set the fetched UserExercise entitiy's property userRoutine to your routine (and don't forget to save the changes in your managed object context).
myRoutine.userexercises = orphanedExercises
Later, if you want to get the exercises for a particular routine:
let fetchRequest = NSFetchRequest(entityName: "UserExercises")
fetchRequest.predicate = NSPredicate(format: "userroutine == %#", someUserRoutine)