Best way to implement Enums with Core Data

Question

What is the best way to bind Core Data entities to enum values so that I am able to assign a type property to the entity? In other words, I have an entity called Item with an itemType property that I want to be bound to an enum, what is the best way of going about this.

Answer 1

You'd have to create custom accessors if you want to restrict the values to an enum. So, first you'd declare an enum, like so:

typedef enum {
    kPaymentFrequencyOneOff = 0,
    kPaymentFrequencyYearly = 1,
    kPaymentFrequencyMonthly = 2,
    kPaymentFrequencyWeekly = 3
} PaymentFrequency;

Then, declare getters and setters for your property. It's a bad idea to override the existing ones, since the standard accessors expect an NSNumber object rather than a scalar type, and you'll run into trouble if anything in the bindings or KVO systems try and access your value.

-(PaymentFrequency)itemTypeRaw {
    return (PaymentFrequency)[[self itemType] intValue];
}

-(void)setItemTypeRaw:(PaymentFrequency)type {
    [self setItemType:[NSNumber numberWithInt:type]];
}

Finally, you should implement +keyPathsForValuesAffecting<Key> so you get KVO notifications for itemTypeRaw when itemType changes.

+(NSSet *)keyPathsForValuesAffectingItemTypeRaw {
    return [NSSet setWithObject:@"itemType"];
}

Answer 2

An alternative approach I'm considering is not to declare an enum at all, but to instead declare the values as category methods on NSNumber.