Core Data Extensions for SwiftUI

CoreDataExtensions.swift

class RingEditViewModel: ObservableObject {

    @NestedObservableObject var ring: RingData

    private let isEditing: Bool
    private let temporaryContext: NSManagedObjectContext

    init(context: NSManagedObjectContext, ring: RingData? = nil) {
        self.temporaryContext = context.child()
        if let ring = temporaryContext.copy(of: ring) {
            self.ring = ring
            self.isEditing = true
        } else {
            self.ring = temporaryContext.instance()
            self.isEditing = false
        }
    }

    var pageTitle: String {
        isEditing ? "Edit Ring" : "Add Ring"
    }

    var saveButtonTitle: String {
        isEditing ? "Save Changes" : "Add Ring"
    }

    func persist() {
        try? ring.persist()
    }

}

extension NSManagedObjectContext {

    func child() -> NSManagedObjectContext {
        let child = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
        child.parent = self
        return child
    }

    func copy<T:NSManagedObject>(of object: T?) -> T? {
        guard let object, let copy = (try? existingObject(with: object.objectID)) as? T else {
            return nil
        }
        return copy
    }

    func instance<T:NSManagedObject>() -> T {
        T(context: self)
    }

}

extension NSManagedObject {

    func persist() throws {
        if hasChanges {
            try managedObjectContext?.save()
            try managedObjectContext?.parent?.save()
        }
    }

}