The Core Data Stack - Core Data - page 50

context . persistentStoreCoordinator = psc
//4
let documentsURL = applicationDocumentsDirectory ()
let storeURL =
documentsURL. URLByAppendingPathComponent ( "Dog Walk" )
let options =
[ NSMigratePersistentStoresAutomaticallyOption : true ]
var error: NSError ? = nil
store = psc . addPersistentStoreWithType ( NSSQLiteStoreType ,
configuration: nil ,
URL: storeURL,
options: options,
error:&error)
if store == nil {
println ( "Error adding persistent store: \(error) " )
abort ()
}
}
The initializer is responsible for configuring each individual component in your Core
Data stack. It's a large chunk of code that probably looks very cryptic at the
moment, so let's go over each section in turn:
1. The first step is to load the managed object model from disk into a
NSManagedObjectModel object. You do this by getting a URL to the momd directory
that contains the compiled version of the .xcdatamodeld file.
2. Once you've initialized NSManagedObjectModel , the next step is to create
NSPersistentStoreCoordinator . Remember that the persistent store coordinator
mediates between the persistent store and NSManagedObjectModel . Initialize one
using the NSManagedObjectModel you just created.
3. The NSManagedObjectContext takes no arguments to initialize. However, it won't
be very useful until you connect it to an NSPersistentStoreCoordinator . You can
do this easily by setting the context's persistentStoreCoordinator property to the
persistent store coordinator you just created in the previous step.
4. The way you create a persistent store is a bit unintuitive—you don't initialize it
directly. Instead, the persistent store coordinator hands you an
NSPersistentStore object as a side effect of attaching a persistent store type. You
simply have to specify the store type ( NSSQLiteStoreType in this case), the URL
location of the store file and some configuration options.