Updater class to migrate to a new CoreData model

Updater.m

#import "Updater.h"
#import "SemesterOld.h"
#import "Semester.h"

#import "Fach.h"
#import "Subject.h"

@interface Updater ()	
- (void)setupOldStack;
- (void)setupNewStack;

/**
 Does the whole migration.
 */
- (void)migrate;

@end

@implementation Updater {
    // Old Core Data stack
    NSManagedObjectContext *oldContext;
    NSPersistentStoreCoordinator *oldStoreCoordinator;
    NSManagedObjectModel *oldObjectModel;
    NSURL *oldDatabaseFile;	    
    // New Core Data Stack
    NSManagedObjectContext *newContext;
    NSPersistentStoreCoordinator *newStoreCoordinator;
    NSManagedObjectModel *newObjectModel;
    NSURL *newDatabaseFile;
}

- (void)update
{
    // URLs of the old and the new (temporary) database files.
    NSFileManager *manager = [NSFileManager defaultManager];
    newDatabaseFile = [NSURL fileURLWithPath: [[manager libraryDirectory] stringByAppendingPathComponent: @"Database.sqlite"]];
    oldDatabaseFile = [NSURL fileURLWithPath: [[manager documentsDirectory] stringByAppendingPathComponent: @"Database.sqlite"]];
    
    // If the old database file does not exist, just skip it!    
    if (![manager fileExistsAtPath:[oldDatabaseFile path]]) {
        return;
	}
	    
	// Setup both stacks.
    [self setupOldStack];
    [self setupNewStack];
    
    [self migrate];
}
	
#pragma mark Migration
	
- (void)migrate
{
    // We migrate only the data that the user still needs.
    NSArray *oldSemesters = [SemesterOld MR_findAllInContext:oldContext];
    
    // Create new Semesters
    for (SemesterOld *semester in oldSemesters) {
        Semester *newSemester = [Semester MR_createInContext:newContext];
        newSemester.name = semester.name;
        
        // ...
    }
    
    [newContext save:nil];
}
	
#pragma mark Setup

- (void)setupNewStack
{
    NSURL *url = [[NSBundle mainBundle] URLForResource:@"Database2" withExtension:@"momd"];
    newObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:url];
    
	NSError *error;
	newStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:newObjectModel];
		
	NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
							 [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
							 [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];
		
	if (![newStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType
	                                          configuration:nil URL:newDatabaseFile
	                                                options:options error:&error]) {
		NSLog(@"Error with lodaing persistentstore: %@ , Userinfo: %@", error , [error userInfo]);
	}
		
    newContext = [NSManagedObjectContext MR_contextWithStoreCoordinator:newStoreCoordinator];
}
 
- (void)setupOldStack
{
    NSURL *url = [[NSBundle mainBundle] URLForResource:@"Database1" withExtension:@"momd"];
    oldObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:url];
		
	NSError *error;
	oldStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:oldObjectModel];
		
	NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
							 [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
							 [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];
		
	if (![oldStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType
												  configuration:nil URL:oldDatabaseFile
													options:options error:&error]) {
		NSLog(@"Error with lodaing persistentstore: %@ , Userinfo: %@", error , [error userInfo]);
	}
		
	oldContext = [NSManagedObjectContext MR_contextWithStoreCoordinator:oldStoreCoordinator];
}
	
	
@end