Insert data with MagicalRecord - objective-c

Question

I am using CoreData with MagicalRecord.
I'd like to insert Data in following code, but to insert data become an error with a message Cocoa error 133000.
AppDelegate.m
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
[MagicalRecord setupCoreDataStackWithAutoMigratingSqliteStoreNamed:#"class_schedule.sqlite"];
return YES;
}
ViewController.m
- (void)saveData
{
Data *data = [Data MR_createEntity];
[MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {
Data *localData = [data MR_inContext:localContext];
localData.title = textField.text;
} completion:^(BOOL success, NSError *error) {
}];
}
Data.h
#interface Data : NSManagedObject
#property (nonatomic, retain) NSNumber * id;
#property (nonatomic, retain) NSString * title;
#end
Can you tell me how to insert record with Magical Record?

Answer 1

Error:
Cocoa error 133000 is:
NSManagedObjectReferentialIntegrityError = 133000, // attempt to fire a fault pointing to an object that does not exist (we can see the store, we can't see the object)
(Taken from this SO question). Basically you are doing something with a NSManagedObject that doesn't exist.
Inserting data:
In terms of how to insert data using magical record take a look at this tutorial which will probably explain it much better than I can.
My advice:
Use Core Data straight up. It's quite a steep learning curve, but very quickly becomes intuitive and easy to use. It will also stand you in good stead if you know how it all works rather than relying on a third party.
If you're interested in how it works at a more fundamental level, take a look at SQLite. I wouldn't necessarily recommend using it as it is a C library but it will help you get a deeper understanding.

Answer 2

You get error 133000 when you try to access object that is not existing. "But hey", you might say, "what do you mean not existing? I'm creating it right there!".
When you are creating NSManagedObject like you do, that is with MR_createEntity, under the hood it calls
NSManagedObject *newEntity = [self MR_createEntityInContext:[NSManagedObjectContext MR_contextForCurrentThread]]
This context is not saved in any way by doing that, and created entity is not persisted. Then by calling
Data *localData = [data MR_inContext:localContext];
You are actually making this under the hood:
BOOL success = [[self managedObjectContext] obtainPermanentIDsForObjects:#[self] error:&error];
The problem is that if NSManagedObject isn't persisted, you won't get persistent ID that is next used in
NSManagedObject *inContext = [otherContext existingObjectWithID:[self objectID] error:&error];
Above method fails to retrieve existing object because it's not existing in store yet (remember, context for current thread in which created entity exists is not saved at any point).
But worry not, fix for this is pretty simple. Don't create new entity like that. Instead do it like this:
[MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {
Data *localData = [data MR_createEntityInContext:localContext];
localData.title = textField.text;
} completion:^(BOOL success, NSError *error) {
}];
That way create entity and modify in context that is going to be saved immediately. This is the correct way to create entities in MagicalRecord.