# Unique(_:) Specifies the key-paths that SwiftData uses to enforce the uniqueness of model instances. ``` @freestanding(declaration) macro Unique(_ constraints: [PartialKeyPath]...) where T : PersistentModel ``` ## Parameters `constraints` Arrays of model key-paths that form the unique constraints to apply to the enclosing model. ## Overview If a model class contains attributes that you require to be unique across all persisted instances of that model, add the `Unique` macro to that model’s definition. You can specify a constraint on a single attribute, a compound constraint across multiple attributes, or any combination of the two. > Important: For relationship attributes, SwiftData only supports unique > constraints on those that reference a single persistent model, rather than an > array of persistent models. The following example declares that every instance of `Person` has a unique `id`, and that no two instances of `Person` have the same `givenName` and `familyName`: ```swift @Model final class Person { // Declare any unique constraints as part of the model definition. #Unique([\.id], [\.givenName, \.familyName]) var id: UUID var givenName: String var familyName: String init(id: UUID, givenName: String, familyName: String) { self.id = id self.givenName = givenName self.familyName = familyName } } ``` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)