Core Data list relationship of Parent Object - ios

Question

i have two Core-Data entities. One called "Program" and one called "Exercise". Program has a one-to-many relationship to Exercise.
I add Exercises to a Program in another view.
I have one view with all the programs listed and a navigation link which leads to this view.
In this view I want to list all the exercises I assigned earlier to the program. However if I try this code, I get the error message: Generic struct 'ForEach' requires that 'Exercise' conform to 'RandomAccessCollection'.
I am new to Core Data Relationships and think I might have forgotten to declare something in the CoreDataClass File. The Problem is that I cant find any other solutions to this question.
struct ProgramView: View {
#ObservedObject var ProgramDetail: Program
var body: some View {
List {
ForEach(ProgramDetail.exercise!, id: \.self) { exercise in
Text(exercise.name!)
}
}
This generates the List of all Programs:
struct ProgramList: View {
#Environment(\.managedObjectContext) var viewContext
#FetchRequest(sortDescriptors: [NSSortDescriptor(keyPath: \Program.date, ascending: false)]) var programFetch: FetchedResults<Program>
var body: some View {
NavigationView {
List {
ForEach(programFetch, id: \.self) { program in
NavigationLink(destination: ProgramView(ProgramDetail: program)) {
Text(program.title!)
}
}
}.navigationBarItems(
trailing:
NavigationLink(destination: CreateProgram()) {
Image(systemName: "plus.circle").font(.system(size: 25))
})
}
}
Here is a screenshot of the Interface?:
Interface

Answer 1

The error message is explaining that you must have a Random Access Collection, so that ForEach can iterate through the collection.
For example, Swift's Array conforms to RandomAccessCollection protocol, so you could use an array.
I'd suggest that you read up on collections, either in the Swift documentation or on Apple's Developer website.
There are probably a few ways to achieve a solution, but perhaps the easiest method is as follows...
struct ProgramView: View {
#ObservedObject var programDetail: Program
#FetchRequest(entity: Exercise.entity(),
sortDescriptors: [NSSortDescriptor(keyPath: \Exercise.name, ascending: true)],
) var allExercises: FetchedResults<Exercise>
var body: some View {
List {
// in this line you create an array of fetched results
// filtered to contain only exercises for programDetail
let exercisesForProgram = allExercises.filter { $0.program == programDetail }
ForEach(exercisesForProgram) { exercise in
Text(exercise.name!)
}
}
}
}

Answer 2

Assuming you haven't changed the Arrangement of your To Many relationship to Ordered, ProgramDetail.exercise is an NSSet?.
You could define a computed property to transform it to an Array of Exercise:
extension Program {
var exerciseArray: [Exercise] {
let sortDescriptor = NSSortDescriptor(key: "name", ascending: true)
return exercise?.sortedArray(using: [sortDescriptor]) as? [Exercise] ?? [Exercise]()
}
}
In ProgramView now you could then create your List using the Array as follows:
List {
ForEach(programDetail.exerciseArray, id: \.self) { exercise in
Text("\(exercise.name ?? "")")
}
}
In case exercise is an Ordered relationship, then ProgramDetail.exercise will be an NSOrderedSet?.
In this case the definition of exerciseArray is even simpler:
var exerciseArray: [Exercise] {
return exercise?.array as? [Exercise] ?? [Exercise]()
}