Core Data: Create multiple managed objects, but only save some?

I'm trying to write a favorites system for my app. I've already converted my model to a managed object. So imagine the user is presented a screen with a list of such objects. They can choose to save some to their favorites, which will persist them in core data.

The problem is, when I create all of these model objects, I do so with the managed object context. If the user saves a single one to their favorites, it's going to save the whole context, and persist every single entity. The extras won't be in their favorites, since adding to favorites constructs a "favorite" entity that gets saved开发者_开发技巧 and points to the object, which the others won't have. But all of the other objects will be saved needlessly.

What's the standard way out of this / standard way to design an iPhone favorites system? Should I separate my model into two classes, the one I show the user, and then one that saves to the db? That way I could construct my models without putting them into the MOC. But that would be a duplicated class with all the same fields.

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There is not really a standard way to do this because Core Data expects you to save the objects you create. However, if you create the objects with:

id object = [[NSManagedObject alloc] initWithEntityDescription:entity inManagedObjectContext:nil];

They won't have a context to save against. Then for the ones you need to save you can:

[[self managedObjectContext] insertObject:object];

Then call -save: on the context and only those that have had their context set will save.

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Wouldn't it be easier to have an isFavorite property on your managed objects. Then in your favorites view you can filter based on that?