How to make transient attributes in a SwiftData model 관련

SwiftData by Example

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How to make transient attributes in a SwiftData model | SwiftData by Example

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How to make transient attributes in a SwiftData model

Updated for Xcode 15

SwiftData automatically saves all stored property into its data storage. If you don’t want that – if you have temporary data that is needed only while your program is running – then you can mark it using the @Transient macro so that SwiftData treats it as ephemeral and disposable, so it won’t be saved along with the rest of your data.

For example, if you were building a game, you might want to track how many levels a player has completed in the current run so you can suggest they take a break after a while, like this:

@Model class Player {
    var name: String
    var score: Int
    @Transient var levelsPlayed = 0

    init(name: String, score: Int) {
        self.name = name
        self.score = score
    }
}

That starts with a default value of 0 when your app runs, and will automatically reset to 0 when the app terminates – it won’t be stored inside SwiftData.

SwiftData automatically saves only the stored properties of your models – any computed properties are automatically transient. For example, if we wanted to put our Player model into a high score table, we might add a computed property that shows both their name and score:

@Model class Player {
    var name: String
    var score: Int
    @Transient var levelsPlayed = 0

    var highScoreEntry: String {
        "\(name) scored \(score) points"
    }

    init(name: String, score: Int) {
        self.name = name
        self.score = score
    }
}

There are two important things to remember when working with transient properties in SwiftData:

1. Transient properties cannot be used in SwiftData query predicates because the actual data you’re working with doesn’t exist on disk. Attempting to use a transient property will compile just fine, but crash at runtime.
2. Transient properties must always have a default value as shown above, so that when you create a new object or when an existing one is fetched from disk, there’s always a value present.