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iPhone Core data - Not constant path between entities

Answer 1

A:

Add a nil check on the relationship then...

if (user.menu != nil && user.menu.meal != nil)

Or even better, define a helper method that will return the meal if it's present...

mealForUser:(User*)someUser {
     if (user.menu != nil && user.menu.meal != nil)
     return user.menu.meal;
}

mmccomb 2010-04-20 11:45:19

The problem is that I have some to many relationships and can't check each of the menus and meals... don't you have a better solution to implement IN the NSPredicate?

ncohen 2010-04-20 11:51:24

You can perform similar checks in your NSPredicate. If you have a FetchRequest for the entity user then you can specify a NSPredicate as follows...predicate = [NSPredicate predicateWithFormat:@"(menu != nil) AND (menu.meal != nil)"];

mmccomb 2010-04-20 12:44:28

Ok but let say some of my users have menus and some of these menus have meals. How would you do with these 'one to many' relationships?

ncohen 2010-04-20 12:58:35

To deal with one-to-many relationships you can use....[NSPredicate predicateWithFormat:@"(menu != nil) AND (menu.meals@count > 0)"]

mmccomb 2010-04-20 13:21:01

That is a lot of dancing just to use dot syntax when a simple KVC call will work.

Marcus S. Zarra 2010-04-20 17:57:58

Answer 2

A:

First, you can check this in code as:

if (![user valueForKeyPath:@"menu.meal"]) {
 //User does not have a menu or a meal
}

Inside of your predicate it would look the same:

[NSPredicate predicateWithFormat:@"user.menu.meal == nil"]

In either case, because nil is handled gracefully in Objective-C you will get the right answer.

Marcus S. Zarra 2010-04-20 17:56:57

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iPhone Core data - Not constant path between entities

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