I am trying to learn swiftdata, and I am struggling with relationships, in SQL it is very straightforward, but I don’t understand why the relationship I have set up works, it seems to but why?

These are the two data models that I have set up for a one to may relartionship:

@Model
final class meals {
    
    @Relationship(deleteRule: .cascade, inverse: readings.whichMeal) var whichMeal: [readings]
    var mealDesc: String
    
    init(whichMeal: [readings], mealDesc: String){
        self.whichMeal = whichMeal
        self.mealDesc = mealDesc
    }
}

@Model
final class readings {
    var readDate: Date
    var whichMeal: meals
    var comment: String
    var glucoseReading: Float
    var ketoneReading: Float?
    
    init(readDate: Date,
         whichMeal: meals,
         comment: String,
         glucoseReading: Float,
         ketoneReading: Float
    ){
        self.readDate = readDate
        self.whichMeal = whichMeal
        self.comment = comment
        self.glucoseReading = glucoseReading
        self.ketoneReading = ketoneReading
    }
    
}

My question is how does SwiftData know that “whichMeal” in both models is an integer?