How to make transient attributes in a SwiftData model
How to make transient attributes in a SwiftData model 관련
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:
- 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.
- 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.
