Is there any reason why someone would want to create an Core Data model programmatically?

Question

I wonder in which cases it would be good to make an NSManagedObjectModel completely programmatically, with NSEntityDescription instances and all this stuff.

I'm that kind of person who prefers to code programmatically, rejecting Interface Builder. But when it comes to Core Data, I have a hard time figuring out why I should kill my time NOT using the nice Xcode Data Modeler tool.

And since data models are stuck to a given state (except when you want to do some ugly migration operations where thinks probably go wrong and users get mad, really mad), I see no big sense in a data model that's made programmatically for the purpose of changing it all the time.

Did I miss something?

Answer 1

I dont think you missed anything. The only reason I can see to create your model programatically would be if the objects you are modeling are themselves dynamic: you could for instance build a coredata entity (or graph of entities) in response to a web service which changed over time, or was selected by the user. However, I think if you had that or a similar use case, you wouldn't need to write this question (and you'd probably solve it a different way anyway)

Answer 2

Everything is a trade off. Basically, I think IB and the visual Core Data modeler are the right tool if you're building a simple application. You'll need to make the determination when your application becomes large/complex enough that you prefer to have direct control over all aspects of the code.

Regarding Interface Builder, if you have an application with a variety of complex interactions between view controllers, and multiple custom controls, I find code more appropriate.

For Core Data, the question is pretty much the same. Does your project have a defined scope? Can you foresee everything in that scope being done within the visual modeler? If so, it's probably fine. For other projects, where you may be asked to add features on an ongoing basis, perhaps it's better to spend a little more time writing it out so you have more flexibility later.

One other thing to consider, that doesn't get mentioned much, is it's MUCH harder to ask for help with IB or any hybrid visual design/code system. When something does go wrong, or you need help, it's way easier to post your code, than try to explain what's going on in a visual modeler.

Answer 3

In general, there's no reason to build the managed object model in code. There's nothing you can do in code that can't be done in the model editor. There are some fancy tricks you can do in code, however, to work with multiple models. For example, you can merge two models, establishing cross-model relationships between entities in those models at load time (see http://stackoverflow.com/questions/130316/cross-model-relationships-in-nsmanagedobjectmodel-from-merged-models).

Regarding whether it's a good idea to code or use the graphical editor, I think the balance tips heavily towards the graphical editor in this case. Being able to verify the model by visual inspection instead of (rather convoluted) code is a win. The model can still be verified by unit test, if you desire.