Swift 3 - Core Data Saving with one-to-many relationship

Question

I'm working with core data and i have two entity:

SwimmingPool Parameters Each swimming pool can have multiple parameters

I have already saved and fetched data for swimming pool.

I've saved them trough a form.

In my AppDelegate i have:

let ad = UIApplication.shared.delegate as! AppDelegate
let context = ad.persistentContainer.viewContext

and here's the func:

 var swimmingpool: SwimminPool!

    if swimmingPoolToEdit == nil {
        swimming = SwimminPool(context: context)
    } else {
        swimming = swimmingPoolToEdit
    }

    if let name =  swimmingName.text {
        swimming.name = name
    }
    if let volume = swimmingVolume.text {
        swimming.volume = volume
.........................................................
ad.saveContext()

and i perform the fetch like so:

var controller: NSFetchedResultsController<SwimmingPool>!

func attemptFetch() {

    let fetchRequest: NSFetchRequest<SwimminPool> = SwimminPool.fetchRequest()
    let dataSort = NSSortDescriptor(key: "createdAt", ascending: false)

    fetchRequest.sortDescriptors = [dataSort]

     let controller = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)

    controller.delegate = self
    self.controller = controller

    do {
        try controller.performFetch()
    } catch {
        let error = error as NSError
        print("\(error.debugDescription)")
    }
}

Through a segue i pass all the data to a new controller and through a new form (in an another controller) i'm trying to save the data for the parameters and connect them to the the specific swimming pool.

Do i need to save the data like i did for the swimming pool and the relationship will automatically connect the two entities or do i need to connect them upon saving?

I'm new to swift and i'm not sure how to save related datas

The connection will be made upon saving or when i will perform the parameters fetch?

Thank you!

Answer 1

Create Parameter managed object and then link this parameter to a SwimingPool managed object:

let parameter = Parameters(context: context)
parameter.chlorum = Double(12245454.12211) // insert your value
parameter.oxigen = "your value here"
parameter.createdAt = "your value here"

let swimming = SwimminPool(context: context)
swimming.parameter = parameter
ad.saveContext()

Answer 2

If you want to add Parameters to a specific SwimmingPool

• In the segue pass the specific SwimmingPool instance to the form controller.
• Create Parameters instances by inserting them into the context.
• Add the relationship to the SwimmingPool instance by calling insert on the parameter attribute / relationship or the generated accessor addToParameter of the NSManagedObject subclass.
• Save the context. (important as last step).

Note : To avoid confusion name an Entity always in singular form (e.g. SwimmingPool / Parameter), a one-to-one relationship also in singular form (e.g. parameter) and a one-to-many relationship in plural form (e.g. parameters)

PS: You question is ambiguous: You are writing Each swimming pool can have multiple parameters but the model design is Each parameter can have multiple swimming pools