Question

Writing my first app with CoreData. The book I’m using to guide me has code like this:

// 'Person' is my managed object class
Person *newPerson = [NSEntityDescription
  insertNewObjectForEntityForName:@"Person"
  inManagedObjectContext:self.managedObjectContext];

[newPerson setValue:nameField.text forKey:@"name"];

The book says that using the property style, e.g.

newPerson.name = nameField.text;

also works, but that “it is very common to see Core Data code use the KVC Approach”

To me, I can’t see one reason to use the KVC approach; magic strings just beg for runtime errors and it’s a lot more typing.

That being said, I’d like to learn my habits now regarding the “iPhone Way” of doing things.

Is there a difference in these approaches and, if most people use the first, KVC, approach…why?

Answer 1

Most people do not use the KVC approach I have seen; I do not, for the reasons you describe.

To save your sanity, use Mogenerator to build your accessors:

http://rentzsch.github.com/mogenerator/

It’s a command line tool that generates proxy objects that you can use to fetch CoreData objects, with some convenience methods – but even better, some category overlays that you can add your own methods to that will not be destroyed when you re-generate classes from your data model.

XCode can also generate data objects from your model but the classes are more simple (just accessors), and mogenerator is I think easier to use repeatedly (which is important since you will tend to change the model a lot over time). Perhaps the next XCode will be better in that regard.

I usually generate all data model classes into a subdirectory under Classes called “DataObjects” – then you can just re-add that whole directory every time you regenerate classes from the data model that leads to new classes being created (when you have new entities). A sample command line run looks like:

 mogenerator -m ../MyProject.xcdatamodeld/MyProject-v1.xcdatamodel

which will generate classes into the current directory from the given data model (in that case I have a versioned model with just the first version).