iOS: Coredata backups - Anything to pay attention to? - ios

Question

I'm using coredata in my app and want to offer the possibility to create and restore safety copies. My process is relatively simple:
- The user can just create a copy of the current active database, this is a new backup
- If he chooses to restore a backup, then there will be a safety copy of the current active database created, then the active database will be deleted and the selected safety copy will be copied and renamed to the previous active database name. Does this work that simple or are there any traps?
Here's my code:
#pragma mark Database methods
- (BOOL)createSafetyCopy: (void (^)(void))completionHandler
{
NSFileManager *fileManager = [NSFileManager defaultManager];
NSError *error;
NSString *dbPath = [self getFullDBPathAsString];
if([fileManager fileExistsAtPath:dbPath]) {
//Create the timestamp
NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:#"yyyyMMdd"];
NSDateFormatter *timeFormat = [[NSDateFormatter alloc] init];
[timeFormat setDateFormat:#"HHmmss"];
NSDate *now = [[NSDate alloc] init];
NSString *timeStamp = [NSString stringWithFormat:#"%#_%#", [dateFormat stringFromDate:now], [timeFormat stringFromDate:now]];
NSString *copyPath = [[self.applicationDocumentsDirectory URLByAppendingPathComponent:[NSString stringWithFormat:#"%#%#", timeStamp, kSafetyCopySuffix]] path];
bool success = [fileManager copyItemAtPath:dbPath toPath:copyPath error:&error];
if (!success){
NSLog(#"Failed to create safety copy with message '%#'.", [error localizedDescription]);
return FALSE;
} else {
completionHandler();
}
} else {
NSLog(#"Active database doesn't exist at path: %#", dbPath);
return FALSE;
}
return TRUE;
}
- (NSArray *)getListOfSafetyCopies
{
NSFileManager *manager = [NSFileManager defaultManager];
//get the apps documents directory
NSString *documentsDirectory = [self.applicationDocumentsDirectory path];
// grab all the files in the documents dir
NSArray *allFiles = [manager contentsOfDirectoryAtPath:documentsDirectory error:nil];
// filter the array for only safety copies
NSPredicate *filter = [NSPredicate predicateWithFormat:#"self ENDSWITH %#", kSafetyCopySuffix];
NSArray *safetyCopies = [allFiles filteredArrayUsingPredicate:filter];
return safetyCopies;
}
- (BOOL)restoreSafetyCopy:(NSString *)safetyCopyName
{
NSFileManager *fileManager = [NSFileManager defaultManager];
NSError *error;
NSString *fullSafetyCopyPath = [[self.applicationDocumentsDirectory URLByAppendingPathComponent:safetyCopyName] path];
if([fileManager fileExistsAtPath:fullSafetyCopyPath]){
//create safety copy of currently active database
//[self createSafetyCopy];
//Then delete active database
if ([fileManager removeItemAtPath:[self getFullDBPathAsString] error:&error]){
//And if successfull replace it with the safety copy;
if (![fileManager copyItemAtPath:fullSafetyCopyPath toPath:[self getFullDBPathAsString] error:&error]){
NSLog(#"Failed to restore safety copy with message '%#'.", [error localizedDescription]);
return FALSE;
}
} else {
NSLog(#"Failed to delete active database with message '%#'.", [error localizedDescription]);
return FALSE;
}
} else {
NSLog(#"Safety copy doesn't exist at path: %#", fullSafetyCopyPath);
return FALSE;
}
return TRUE;
}

Answer 1

CoreData data is not stored only in single sql file. In my DB folder I see 3 files: Model.sqlite, Model.sqlite-shm, Model.sqlite-wal.
You can read about WAL-journal, but as far as I know, you can't rely only on copying 1 sqlite file. Some data (transactions) is stored in WAL.
Actually you can read about it here:
Technical Q&A QA1809