我正在使用以下代码创建一个对象：
+(Checkin *) newCheckinWithId:(NSString*) checkinID forVenueId:(NSString *)venueId
{
NSManagedObjectContext * context = [[AppDelegate sharedInstance] managedObjectContext];
Checkin *ret = (Checkin *)[NSEntityDescription insertNewObjectForEntityForName:@"Checkin" inManagedObjectContext:context];
ret.checkinID = checkinID;
ret.forVenueID = venueId;
ret.date = [NSDate date];
NSError * error;
if(![context save:&error]) {
NSLog(@"Error saving!!!!!: %@", error.userInfo);
}
return ret;
}
此代码有效，我可以在磁盘上的 sqldatabase 文件中看到对象（在 ~/library/iphone sim/.. 不管它是什么）
这是我用来创建商店 + 托管对象上下文的代码（我对所有内容都使用 1 个上下文）它基本上全部来自我发现的堆栈溢出帖子
- (NSManagedObjectModel *)managedObjectModel
{
if (_managedObjectModel != nil)
{
return _managedObjectModel;
}
//NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Model" withExtension:@"momd"];
//__managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
//NSArray *testArray = [[NSBundle mainBundle] URLsForResourcesWithExtension:@"momd"subdirectory:nil];
NSString *path = [[NSBundle mainBundle] pathForResource:@"Model" ofType:@"momd"];
if( !path ) path = [[NSBundle mainBundle] pathForResource:@"Model" ofType:@"mom"];
NSURL *modelURL = [NSURL fileURLWithPath:path];
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
//__managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil];
return _managedObjectModel;
}
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
if((_persistentStoreCoordinator != nil)) {
return _persistentStoreCoordinator;
}
_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel: [self managedObjectModel]];
NSPersistentStoreCoordinator *psc = _persistentStoreCoordinator;
// Set up iCloud in another thread:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// ** Note: if you adapt this code for your own use, you MUST change this variable:
NSString *iCloudEnabledAppID = @"[MY APP ID]";
// ** Note: if you adapt this code for your own use, you should change this variable:
NSString *dataFileName = @"foursquareaugmentation.sqlite";
// ** Note: For basic usage you shouldn't need to change anything else
NSString *iCloudDataDirectoryName = @"Data.nosync";
NSString *iCloudLogsDirectoryName = @"Logs";
NSFileManager *fileManager = [NSFileManager defaultManager];
NSURL *localStore = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:dataFileName];
NSURL *iCloud = [fileManager URLForUbiquityContainerIdentifier:nil];
if (iCloud) {
NSLog(@"iCloud is working");
NSURL *iCloudLogsPath = [NSURL fileURLWithPath:[[iCloud path] stringByAppendingPathComponent:iCloudLogsDirectoryName]];
NSLog(@"iCloudEnabledAppID = %@",iCloudEnabledAppID);
NSLog(@"dataFileName = %@", dataFileName);
NSLog(@"iCloudDataDirectoryName = %@", iCloudDataDirectoryName);
NSLog(@"iCloudLogsDirectoryName = %@", iCloudLogsDirectoryName);
NSLog(@"iCloud = %@", iCloud);
NSLog(@"iCloudLogsPath = %@", iCloudLogsPath);
if([fileManager fileExistsAtPath:[[iCloud path] stringByAppendingPathComponent:iCloudDataDirectoryName]] == NO) {
NSError *fileSystemError;
[fileManager createDirectoryAtPath:[[iCloud path] stringByAppendingPathComponent:iCloudDataDirectoryName]
withIntermediateDirectories:YES
attributes:nil
error:&fileSystemError];
if(fileSystemError != nil) {
NSLog(@"Error creating database directory %@", fileSystemError);
}
}
NSString *iCloudData = [[[iCloud path]
stringByAppendingPathComponent:iCloudDataDirectoryName]
stringByAppendingPathComponent:dataFileName];
NSLog(@"iCloudData = %@", iCloudData);
NSMutableDictionary *options = [NSMutableDictionary dictionary];
[options setObject:[NSNumber numberWithBool:YES] forKey:NSMigratePersistentStoresAutomaticallyOption];
[options setObject:[NSNumber numberWithBool:YES] forKey:NSInferMappingModelAutomaticallyOption];
[options setObject:iCloudEnabledAppID forKey:NSPersistentStoreUbiquitousContentNameKey];
[options setObject:iCloudLogsPath forKey:NSPersistentStoreUbiquitousContentURLKey];
[psc lock];
NSError *error;
[psc addPersistentStoreWithType:NSSQLiteStoreType
configuration:nil
URL:[NSURL fileURLWithPath:iCloudData]
options:options
error:&error];
if( error )
{
NSLog(@"Error adding persistent store %@, %@", error, [error userInfo]);
// comment in this line while debugging if get "Can't find model for source store" error in addPersistentStoreWithType.
// it means the sqlite database doesn't match the new model and needs to be created from scratch.
// this happens if you change the xcdatamodel instead of creating a new one under Xcode->Editor->Add Model Version...
// CoreData can only automatically migrate if there is a new model version (it can't migrate if the model simply changes, because it can't see the difference between the two models).
// be sure to back up the database if needed, because all data will be lost.
//[fileManager removeItemAtPath:iCloudData error:&error];
/*// this is another way to verify the hashes for the database's model to make sure they match one of the entries in the momd directory's VersionInfo.plist
NSDictionary *sourceMetadata = [NSPersistentStoreCoordinator metadataForPersistentStoreOfType:NSSQLiteStoreType URL:[NSURL fileURLWithPath:iCloudData] error:&error];
if( !sourceMetadata )
NSLog(@"sourceMetadata is nil");
else
NSLog(@"sourceMetadata is %@", sourceMetadata);*/
}
[psc unlock];
}
else {
NSLog(@"iCloud is NOT working - using a local store");
NSMutableDictionary *options = [NSMutableDictionary dictionary];
[options setObject:[NSNumber numberWithBool:YES] forKey:NSMigratePersistentStoresAutomaticallyOption];
[options setObject:[NSNumber numberWithBool:YES] forKey:NSInferMappingModelAutomaticallyOption];
[psc lock];
NSError *error;
[psc addPersistentStoreWithType:NSSQLiteStoreType
configuration:nil
URL:localStore
options:options
error:nil];
if( error )
NSLog(@"Error adding persistent store %@, %@", error, [error userInfo]);
[psc unlock];
}
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:@"SomethingChanged" object:self userInfo:nil];
});
});
return _persistentStoreCoordinator;
}
/*
Returns the managed object context for the application.
If the context doesn't already exist, it is created and bound to the persistent store coordinator for the application.
*/
- (NSManagedObjectContext *) managedObjectContext
{
if (_managedObjectContext != nil) {
return _managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil) {
_managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
[_managedObjectContext setPersistentStoreCoordinator: coordinator];
}
return _managedObjectContext;
}
这是我的收获：
+(NSArray *) checkinsForVenue:(NSString *) venueID
{
NSManagedObjectContext * context = [[AppDelegate sharedInstance] managedObjectContext];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Checkin" inManagedObjectContext:context];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = entity;
//NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(forVenueID = %@)", venueID];
//request.predicate = predicate;
NSError *error;
NSArray * ret = [context executeFetchRequest:request error:&error];
if(ret == nil) {
NSLog(@"%@", error.description);
}
return ret;
}
即使数据库中有东西，Fetch 总是不返回任何对象（空数组）！
我一直在安静地解决这个问题一段时间，并且非常没有想法，所以任何事情都值得赞赏！
谢谢