+entityForName: nil is not a legal NSManagedObjectContext parameter searching for entity name 'Account''

Question

I have tried a lot of options, but can't find the solution for this problem. I created a Core Data file and named the entity Account, Created an string attribute called username. Then edited the class of the entity to NSManagedObject, not sure if this is right. Now, the following code is in my LoginViewController:

- (void)viewDidLoad
{
    [super viewDidLoad];

    ITAppDelegate *appDelegate = (ITAppDelegate *)[[UIApplication sharedApplication] delegate];
    NSManagedObjectContext *context = appDelegate.managedObjectContext;

    Account *newAccount = [NSEntityDescription insertNewObjectForEntityForName:@"Account" inManagedObjectContext:context];
    [newAccount setValue:@"Jorge" forKey:@"username"];
    [newAccount setPassword:@"password"];

    NSLog(@"username:%@   password: %@", [newAccount username], [newAccount password]);

}

I followed This Tutorial and my code files look like this:

ITAppDelegate.h

#import <UIKit/UIKit.h>

@interface ITAppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;
@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;

@end

ITAppDelegate.m

#import "ITAppDelegate.h"
#import "LoginViewController.h"

@implementation ITAppDelegate

@synthesize managedObjectContext = _managedObjectContext;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
@synthesize managedObjectModel = _managedObjectModel;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary    *)launchOptions
{
    // Override point for customization after application launch.
    return YES;
}

#pragma mark - Core Data stack

- (NSManagedObjectContext *)managedObjectContext
{
if (_managedObjectContext != nil)
{
    return _managedObjectContext;
}

NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil)
{
    _managedObjectContext = [[NSManagedObjectContext alloc] init];
    [_managedObjectContext  setPersistentStoreCoordinator:coordinator];
}
return _managedObjectContext;
}


- (NSManagedObjectModel *)managedObjectModel
{
if (_managedObjectModel != nil)
{
    return _managedObjectModel;
}
NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Model" withExtension:@"momd"];
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
return _managedObjectModel;
}


- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
if (_persistentStoreCoordinator != nil)
{
    return _persistentStoreCoordinator;
}

    return _persistentStoreCoordinator;
}

@end

AccountBase.h

#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>

@interface AccountBase : NSManagedObject

@property (nonatomic, retain) NSString *username;


@end

AccountBase.m

#import "AccountBase.h"

@implementation AccountBase

@dynamic username;

@end

Account.h

#import "AccountBase.h"
#import <CoreData/CoreData.h>

@interface Account : AccountBase

@property (nonatomic, assign) NSString *password;

@end

Account.m

#import "Account.h"
#import "KeychainHelper.h"

@implementation Account

- (NSString*)password
{
    if (self.username)
        return [KeychainHelper getPasswordForKey:self.username];
    return nil;
}

- (void)setPassword:(NSString*)aPassword
{
    if (self.username)
        [KeychainHelper setPassword:aPassword forKey:self.username];
}

- (void)prepareForDeletion
{
    if (self.username)
        [KeychainHelper removePasswordForKey:self.username];
}
@end

KeychainHelper.h

#import <Foundation/Foundation.h>

@interface KeychainHelper : NSObject

+ (NSString*)getPasswordForKey:(NSString*)aKey;
+ (void)setPassword:(NSString*)aPassword forKey:(NSString*)aKey;
+ (void)removePasswordForKey:(NSString*)aKey;

@end

KeychainHelper.m

#import "KeychainHelper.h"
#import <Security/Security.h>

@interface KeychainHelper ()
+ (NSMutableDictionary*)dictionaryForKey:(NSString*)aKey;
@end

@implementation KeychainHelper


static const NSString *ironTrainers = @"com.domain.myapplication";

+ (NSMutableDictionary*)dictionaryForKey:(NSString*)aKey
{
    NSData *encodedKey = [aKey dataUsingEncoding:NSUTF8StringEncoding];

    NSMutableDictionary *searchDictionary = [NSMutableDictionary dictionary];

    [searchDictionary setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];
    [searchDictionary setObject:encodedKey forKey:(__bridge id)kSecAttrGeneric];
    [searchDictionary setObject:encodedKey forKey:(__bridge id)kSecAttrAccount];
    [searchDictionary setObject:ironTrainers forKey:(__bridge id)kSecAttrService];

    return searchDictionary;
}  

+ (NSString*)getPasswordForKey:(NSString*)aKey
{
    NSString *password = nil;

    NSMutableDictionary *searchDictionary = [self dictionaryForKey:aKey];
    [searchDictionary setObject:(__bridge id)kSecMatchLimitOne forKey:(__bridge id)kSecMatchLimit];
    [searchDictionary setObject:(id)kCFBooleanTrue forKey:(__bridge id)kSecReturnData];

    CFTypeRef result = NULL;
    BOOL statusCode = SecItemCopyMatching((__bridge CFDictionaryRef)searchDictionary, &result);
    if (statusCode == errSecSuccess) {
        NSData *resultData = CFBridgingRelease(result);
        password = [[NSString alloc] initWithData:resultData encoding:NSUTF8StringEncoding];
    }
    return (__bridge NSString *)(result);
}

+ (void)removePasswordForKey:(NSString*)aKey
{
    NSMutableDictionary *keyDictionary = [self dictionaryForKey:aKey];
    SecItemDelete((__bridge CFDictionaryRef)keyDictionary);
 }

+ (void)setPassword:(NSString*)aPassword forKey:(NSString*)aKey
{
    [KeychainHelper removePasswordForKey:aKey];

    NSData *encodedPassword = [aPassword dataUsingEncoding:NSUTF8StringEncoding];

    NSMutableDictionary *keyDictionary = [self dictionaryForKey:aKey];
    [keyDictionary setObject:encodedPassword forKey:(__bridge id)kSecValueData];
    SecItemAdd((__bridge CFDictionaryRef)keyDictionary, nil);
}

@end

Any help appreciated. Thanks.

Answer 1

In my case, I'm using multiple contexts (parent/child) with different concurrency types to improve performance. I have three contexts:

1. storeContext which is the only context whose persistentStoreCoordinator had been set.
2. viewContext whose parent is storeContext
3. backgroundContext whose parent should have been viewContext but I forgot to set backgroundContext.parent = viewContext.

Saving an entity on the backgroundContext produced the same error...

+entityForName: nil is not a legal NSManagedObjectContext parameter searching for entity name...

...because backgroundContext wasn't a part of the parent/child context chain.

Setting backgroundContext's parent to viewContext established the chain back to the persistent store coordinator and resolved the error.

Answer 2

- (NSManagedObjectContext *)managedObjectContext
{
    if (managedObjectContext != nil) return managedObjectContext;

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {

        managedObjectContext = [[NSManagedObjectContext alloc] init];
        [managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return managedObjectContext;
}

• You haven't provided a lazy loading implementation of persistentStoreCoordinator
• so coordinator will always be nil
• so you will always be returning nil from this method
• which means you will always get the error above.

To explain the error:

+entityForName: nil is not a legal NSManagedObjectContext parameter searching for entity name 'Account'

It's not immediately obvious from reading it, but this means that nil is not a legal thing to pass for the managed object context. On first reading, it looks like you're doing entityForName:nil but that isn't the case.

To fix the problem, you will need to provide a valid persistent store coordinator. I have a small article here which explains just how little code you need to set up a core data stack, this may help you.