SwiftUI 使用关系预览核心数据

Question

I'm trying to work with Core Data & SwiftUI's previews and think I'm close but haven't been able to get this to work.

    static var previews: some View {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        let newGame = Game.init(context: context)
        newGame.gameName = "Testy Game"
        newGame.gameDescription = "Wooo play the thing"
        newGame.goal = Goal.init(goalName: "Try Harder", goalComplete: false, goalOfGame: newGame)
        return GameGoalsDetail(game: newGame).environment(\.managedObjectContext, context)
    }
}

I'm getting a "Ambiguous reference to member 'init(entity:insertInto:)'" on the newGame.Goal = Goal.init... line.

I'm trying to figure out how to initialize a new Game and then initialize a connected Goal to it right after.

My Core Data Game class takes gameName, gameDescription, and a goal as a NSSet?. The Core Data Goal class has goalName, goalComplete, & goalOfGame: Game?. I think my issue is in connecting the two.

Appreciate the help in advance and willing to share more code if requested.

Answer 1

If they are one-to-many or many-to-many relationship, you can't simply assign the Goal to the Game. When you use core data with relationships you get free "add" methods with the name of your relationship. You should be creating the Goal on one line

let newGoal = Goal.init(goalName: "Try Harder", goalComplete: false)

and then add the newGoal by calling:

newGame.addToGoal(newGoal)

That should take care of any inverse relationship as well.

Answer 2

The Goal is @NSManagedObject thats why you need to use its init with context. When tou create an entity object, you must place it in some store - context is that store. After that you can cast all the properties you need including links.

let goal = Goal(context: context)
goal.goalName = "Try Harder"
goal.goalComplete = false
goal.goalOfGame = newGame
return GameGoalsDetail(game: newGame).environment(\.managedObjectContext, context)

if you set reversed links in data model, there is no need to use add-methods generated by CoreData, if you have at least 1 one-to-one link. You just set this link as a property value and CoreData do all the work for you. goal.goalOfGame is that property - reverced link one-to-one to it parent.

If you realy want to use init with all the property you want to cast, just override it in extention to your class like this:

extention Goal{
    init(of game: Game, name: String = "unnamed", complete: Bool = false, context: NSManagedObjectContext  
    ){
        super.init(context: context)
        self.goalOfGame = game
        self.goalName  = name
        self.complete = goalComplete 
    }
}