I tried to repeat what Paul did in this example. One-to-many relationships with Core Data, SwiftUI, and @FetchRequest However, I got a different result. My result vs. Paul's result

I guess the thing is that I used SwiftUI Life Cycle. How can I fix it?

UPDATE I tried to create new project, but this time based on UIKit App Delegate Life Cycle. And ... the result is the same - a new entity Country is created for each entity Candy (even if it already existed). Xcode 12.3

SOLVED

for UIKit App Delegate Life Cycle: Ensuring Core Data objects are unique using constraints

If you want Core Data to write the changes, you need to open SceneDelegate.swift and add this import:

import CoreData

Now add this line in the willConnectTo method, directly below the code that starts let context:

context.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy

for SwiftUI Life Cycle: SOLVED: Core Data and Lifecycle SwiftUI App

add in Persistence.swift

container.viewContext.automaticallyMergesChangesFromParent = true container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy