I’m reaching out today because I’m having an issue with SwiftData, and I’m on the verge of despair :).

I’m new to SwiftData, and there’s one thing that’s driving me crazy.

I want to save an array that contains several objects conforming to a protocol “Car”, but I’m getting the following error: Type ‘any Car’ cannot conform to ‘PersistentModel’. Here is the complete code:

import Foundation
import SwiftData

protocol Car: Identifiable, Codable, Hashable {
    var id: UUID { get }
    var modelName: String { get}
    var price: Int { get }
}

@Model
class CarSeller: Identifiable {
    var id: UUID
    
    var cars: [any Car]
    
    init(id: UUID, cars: [any Car]) {
        self.id = id
        self.cars = cars
    }
    
    convenience init() {
        self.init(id: UUID(), cars: [])
    }
}

@Model
class Audi: Car {
    
    var id: UUID
    
    var price: Int
    
    var modelName: String
    
    
    init(price: Int, id: UUID, modelName: String) {
        self.price = price
        self.id = id
        self.modelName = modelName
    }
    
    enum CodingKeys: CodingKey {
        case id, modelName, price
    }
    
    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        id = try container.decode(UUID.self, forKey: .id)
        modelName = try container.decode(String.self, forKey: .modelName)
        price = try container.decode(Int.self, forKey: .price)
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(id, forKey: .id)
        try container.encode(modelName, forKey: .modelName)
        try container.encode(price, forKey: .price)
    }
}

@Model
class Mercedes: Car {
    
    var id: UUID
    
    var price: Int
    
    var modelName: String
    
    
    init(price: Int, id: UUID, modelName: String) {
        self.price = price
        self.id = id
        self.modelName = modelName
    }
    
    enum CodingKeys: CodingKey {
        case id, modelName, price
    }
    
    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        id = try container.decode(UUID.self, forKey: .id)
        modelName = try container.decode(String.self, forKey: .modelName)
        price = try container.decode(Int.self, forKey: .price)
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(id, forKey: .id)
        try container.encode(modelName, forKey: .modelName)
        try container.encode(price, forKey: .price)
    }
}

@Model
final class Peugeot: Car {
    var id: UUID
    
    var modelName: String
    
    var price: Int
    
    
    init(price: Int, id: UUID, modelName: String) {
        self.price = price
        self.id = id
        self.modelName = modelName
    }
    
    enum CodingKeys: CodingKey {
        case id, modelName, price
    }
    
    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        id = try container.decode(UUID.self, forKey: .id)
        modelName = try container.decode(String.self, forKey: .modelName)
        price = try container.decode(Int.self, forKey: .price)
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(id, forKey: .id)
        try container.encode(modelName, forKey: .modelName)
        try container.encode(price, forKey: .price)
    }
}

I want to specify that the error appears on this line: var cars: [any Car]

In fact, I found a workaround solution by using an enum, but I didn’t find this solution very elegant.