Clean (remove) a database in MagicalRecord - ios

Question

I have an app that is using MagicalRecord for its Core Data handling and this works nice. However I have different users that can login in the app and when another user logs in, the core data database must be emptied so that the different user can have his own data. The database can be emptied completely as the data is also stored on a webservice and therefore can always be synced again after logging in again the first user.
So far I cannot seem to find a helper method (that works) for this purpose. I have tried
[MagicalRecord cleanUp];
whenever the user is logging out, but this does not do the trick.

Answer 1

This is how I did it. It is essential to have this line: [MagicalRecord cleanup]. Without it, [self setupDB] won't work.
UPDATE: Deletes the -wal and -shm files. #thattyson pointed out an issue in iOS 9. Also, see the answer of #onmyway133.
- (void)setupDB
{
[MagicalRecord setupCoreDataStackWithAutoMigratingSqliteStoreNamed:[self dbStore]];
}
- (NSString *)dbStore
{
NSString *bundleID = (NSString *)[[NSBundle mainBundle] objectForInfoDictionaryKey:(NSString *)kCFBundleIdentifierKey];
return [NSString stringWithFormat:#"%#.sqlite", bundleID];
}
- (void)cleanAndResetupDB
{
NSString *dbStore = [self dbStore];
NSError *error1 = nil;
NSError *error2 = nil;
NSError *error3 = nil;
NSURL *storeURL = [NSPersistentStore MR_urlForStoreName:dbStore];
NSURL *walURL = [[storeURL URLByDeletingPathExtension] URLByAppendingPathExtension:#"sqlite-wal"];
NSURL *shmURL = [[storeURL URLByDeletingPathExtension] URLByAppendingPathExtension:#"sqlite-shm"];
[MagicalRecord cleanUp];
if([[NSFileManager defaultManager] removeItemAtURL:storeURL error:&error1] && [[NSFileManager defaultManager] removeItemAtURL:walURL error:&error2] && [[NSFileManager defaultManager] removeItemAtURL:shmURL error:&error3]){
[self setupDB];
}
else{
NSLog(#"An error has occurred while deleting %#", dbStore);
NSLog(#"Error1 description: %#", error1.description);
NSLog(#"Error2 description: %#", error2.description);
NSLog(#"Error3 description: %#", error3.description);
}
}
Here's the Swift version:
func setupDB() {
MagicalRecord.setupCoreDataStackWithAutoMigratingSqliteStoreNamed(self.dbStore())
}
func dbStore() -> String {
return "\(self.bundleID()).sqlite"
}
func bundleID() -> String {
return NSBundle.mainBundle().bundleIdentifier!
}
func cleanAndResetupDB() {
let dbStore = self.dbStore()
let url = NSPersistentStore.MR_urlForStoreName(dbStore)
let walURL = url.URLByDeletingPathExtension?.URLByAppendingPathExtension("sqlite-wal")
let shmURL = url.URLByDeletingPathExtension?.URLByAppendingPathExtension("sqlite-shm")
var removeError: NSError?
MagicalRecord.cleanUp()
//Swift 1
//let deleteSuccess = NSFileManager.defaultManager().removeItemAtURL(url, error: &removeError)
//Swift 2
let deleteSuccess: Bool
do {
try NSFileManager.defaultManager().removeItemAtURL(url)
try NSFileManager.defaultManager().removeItemAtURL(walURL!)
try NSFileManager.defaultManager().removeItemAtURL(shmURL!)
deleteSuccess = true
} catch let error as NSError {
removeError = error
deleteSuccess = false
}
if deleteSuccess {
self.setupDB()
} else {
println("An error has occured while deleting \(dbStore)")
println("Error description: \(removeError?.description)")
}
}

Answer 2

To expand on #yoninja 's answer, this will make reset CoreData stack explicitly, plus dealing with wal and shm files
- (void)setupDB
{
[MagicalRecord setDefaultModelNamed:#"Model.momd"];
[MagicalRecord setupCoreDataStack];
}
- (void)cleanAndResetupDB
{
[MagicalRecord cleanUp];
NSString *dbStore = [MagicalRecord defaultStoreName];
NSURL *storeURL = [NSPersistentStore MR_urlForStoreName:dbStore];
NSURL *walURL = [[storeURL URLByDeletingPathExtension] URLByAppendingPathExtension:#"sqlite-wal"];
NSURL *shmURL = [[storeURL URLByDeletingPathExtension] URLByAppendingPathExtension:#"sqlite-shm"];
NSError *error = nil;
BOOL result = YES;
for (NSURL *url in #[storeURL, walURL, shmURL]) {
if ([[NSFileManager defaultManager] fileExistsAtPath:url.path]) {
result = [[NSFileManager defaultManager] removeItemAtURL:url error:&error];
}
}
if (result) {
[self setupDB];
} else {
NSLog(#"An error has occurred while deleting %# error %#", dbStore, error);
}
}

Answer 3

MagicalRecord does not provide this functionality for you. The cleanUp method is provided for you to reinitialize your CoreData stack in memory and cleaning up any contexts, queues and other related objects. However, it is not that difficult to do yourself given that MagicalRecord does provide a handy method to get the path for your library.
Check out the -[NSPersistentStore MR_urlForStoreName:] method. This will give you the file url for your store. You can then delete it with an NSFileManager instance. Be careful to do this before you set up the Core Data stack or you'll crash when you save because you'd have yanked out the store from under a properly initialized stack.

Answer 4

The following will completely delete the MagicalRecord CoreData sqlite files, as well as the -wal and -shm files. MagicalRecord puts them all in the Library folder; this will simply remove all files from the folder. This will not work if you have other data you need to persist in the Library folder, I did not:
- (void)resetCoreDataDB
{
[MagicalRecord cleanUp];
[self deleteFilesInLibrary];
[MagicalRecord setupCoreDataStackWithAutoMigratingSqliteStoreNamed:#"YourDBName.sqlite"];
}
- (void)deleteFilesInLibraryDirectory
{
NSString* folderPath = [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSError *error = nil;
for (NSString *file in [[NSFileManager defaultManager] contentsOfDirectoryAtPath:folderPath error:&error])
{
[[NSFileManager defaultManager] removeItemAtPath:[folderPath stringByAppendingPathComponent:file] error:&error];
if(error)
{
NSLog(#"Delete error: %#", error.description);
}
}
}

Answer 5

If you are using the iOS Simulator and deleted the database file, you may probably notice that the data is still there. However, if tested on an actual device (which should be), the file is deleted and the context is reset as should be.
[MagicalRecord cleanUp];
// delete database file
NSError *error;
NSURL *fileURL = [NSPersistentStore MR_urlForStoreName:#"db.sqlite"];
[[NSFileManager defaultManager] removeItemAtURL:fileURL error:&error];
if(error) {
// Hanldle error
}
// reset setup.
[MagicalRecord setupCoreDataStackWithAutoMigratingSqliteStoreNamed:#"db.sqlite"];

Answer 6

A bit rewritten answer of #yoninja for Swift 4:
private var dbStore : String? {
get {
if let bundleId = Bundle.main.bundleIdentifier {
return bundleId + ".sqlite"
}
return MagicalRecord.defaultStoreName()
}
}
func setupCoreDataStack() {
MagicalRecord.setupCoreDataStack(withAutoMigratingSqliteStoreNamed: self.dbStore)
}
func cleanUp() {
MagicalRecord.cleanUp()
var removeError: NSError?
let deleteSuccess: Bool
do {
guard let url = NSPersistentStore.mr_url(forStoreName: self.dbStore) else {
return
}
let walUrl = url.deletingPathExtension().appendingPathExtension("sqlite-wal")
let shmUrl = url.deletingPathExtension().appendingPathExtension("sqlite-shm")
try FileManager.default.removeItem(at: url)
try FileManager.default.removeItem(at: walUrl)
try FileManager.default.removeItem(at: shmUrl)
deleteSuccess = true
} catch let error as NSError {
removeError = error
deleteSuccess = false
}
if deleteSuccess {
self.setupCoreDataStack()
} else {
print("An error has occured while deleting \(self.dbStore)")
print("Error description: \(removeError.debugDescription)")
}
}