You need to add @Relationship to var students: [Student] in Department model, also: import Foundation import SwiftData @Model class Department { ... @Relationship var students: [Student] ... }

With CoreData, I'm able to create fetchRequest based on relationship, for example, fetch all items belong to given box let fetchRequest: NSFetchRequest<Item> = Item.fetchRequest() fetchRequest.predicate = NSPredicate(format: "box == %@", box) but it is not possible with Predicate let predicate = #Predicate<Item> { item in return item.box == box } I wonder, Is there any solution for this?