core data in a static library for the iPhone

Question

I've built a static library that makes heavy use of the Core Data framework. I can successfully use the library in my external project, but ONLY if I include the .xcdatamodel file in the main project. That is less than ideal, since the point of the library was to hide implementation details to the maximum possible.

In a separate question, I was informed that I cannot bundle resources with a library (which makes complete sense to me now).

So is there a way to programatically allow the model to be 'discovered' without having to include the model in the main project?

Answer 1

No, the limitation on using non-Apple frameworks in an iPhone app really changes the dependency game relative to OS X. Most iPhone "frameworks" (e.g. Google's toolbox for Mac, Core Plot, etc.) actually recommend that you include the source in your main application project rather than linking a product (i.e. a static library). I think the community consensus is that, on iPhone, it's OK to expect consumers of your framework to have to do a little "manual" work to use your library. In your case, this is including the xcdatamodel file in the main project. As with most of Objective-C, tell your users not to make use of the implementation details and leave it at that.

Answer 2

I also created my own static library that uses Core Data. Besides the static library I have a another bundle target in the project where I have a Copy Bundle Resources item, that copies some images and things like that into the bundle and a Compile Sources build phase, where I am compiling the xcdatamodel.

The final bundle will contain all the necessary files. In your main project that relies on the static library you have to include that bundle as well. Your main project will now have access to the mom file that is needed to use core data.

To use core data with the mom from the bundle you have to create a merged managed object model in your code (it might be the main project has some core data model as well):

- (NSManagedObjectModel *) mergedManagedObjectModel 
{   
    if (!mergedManagedObjectModel) 
    {
     NSMutableSet *allBundles = [[[NSMutableSet alloc] init] autorelease];
     [allBundles addObjectsFromArray: [NSBundle allBundles]];
     [allBundles addObjectsFromArray: [NSBundle allFrameworks]];

     mergedManagedObjectModel = [[NSManagedObjectModel mergedModelFromBundles: [allBundles allObjects]] retain];
    }

    return mergedManagedObjectModel;
}

By just including the bundle you will not have to give out the xcdatamodel, only the compiled mom file needs to be included.