The 'unique' attribute is a really nice feature, BUT. In some of my apps, the unique identifier for an object is a combination of multiple attributes. (Example: a book title is not unique, but a combination of book title and author list is.)
How do I model this with SwiftData? I cannot use @Attribute(.unique) on either the title OR the author list, but I want SwiftData to provide the same "insert or update" logic.
Is this possible?
I have a similar question also, for now I would create and UUID instead of complex key, e.g.:
@Attribute(.unique) var identifier: UUID
I tested define @Attribute(.unique) multiple times and seems not a correct solution:
@Model final class Book {
@Attribute(.unique)
var title: String
@Attribute(.unique)
var author: String
}
I tried to insert books have some wried result:
container.mainContext.insert(BooK(title: "book 1", author: "author 1"))
try? container.mainContext.save()
// 1 book inserted
container.mainContext.insert(BooK(title: "book 1", author: "author 1"))
try? container.mainContext.save()
// 1 book inserted as expected
container.mainContext.insert(BooK(title: "book 2", author: "author 1"))
try? container.mainContext.save()
// "book 2" replace "book 1", and 1 book is left.
My workaround: create our own unique key with title and author:
@Model final class Book {
@Attribute(.unique)
var titleAndAuthor: String
var title: String
var author: String
init(title: String, author: String) {
self.title = title
self.author = author
titleAndAuthor = self.title + self.author
}
}