Unable to replace one Entity by another in Core Data in iOS

综合技术 2017-12-04 阅读原文

I am working on an iOS application where I am using Core Data for storage. In my store, every entity will be unique, and I'm building a function where I replace one existing entity with another that I pass in. Here is an example of an entity that I pass:

NSManagedObjectContext *context = [[MyDB sharedInstance] managedObjectContext];

    User *user = [NSEntityDescription insertNewObjectForEntityForName:@"User" inManagedObjectContext:context];

    NSNumber *userNumber = 12345;

    user.id = userNumber;
    user.name = @"John Doe";
    user.email = @"[email protected]";
    user.createdDate = [NSDate date];

    [[MyDB sharedInstance] updateUser:user];

Inside my Core Data storage, I have an identical Entity already, except that the email address is "[email protected]". My update at the moment looks like this:

-(void)updateUser:(User *)user {

    NSError *error;
    NSManagedObjectContext *context = [[MyDB sharedInstance] managedObjectContext];

    // Create fetch request
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"User" inManagedObjectContext:context];
    [fetchRequest setEntity:entity];

    // Create predicate
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"id == %@", user.id];
    [fetchRequest setPredicate:pred];

    NSArray *results = [context executeFetchRequest:fetchRequest error:&error];

    if (error) {
        // handle fetch error
    } else {

        user = [[User alloc] initWithEntity:entity insertIntoManagedObjectContext:context];

        for (User *recordToDelete in results) {

            [context deleteObject:recordToDelete];//record gets deleted here, which is fine

        }

        [context save:&error]; //this doesn't save the new entity that I passed in

        if (error) {
            // handle save error
            NSLog(@"Whoops, couldn't save: %@", [error localizedDescription]);
        }

    }

    [fetchRequest setEntity:entity];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"id=%@", 12345];
    [fetchRequest setPredicate:pred];

    NSArray *items = [context executeFetchRequest:fetchRequest error:&error];

    for (User *testObject in items) {

        NSLog(@"ID: %@, Name: %@, Email: %@, Created Date: %@", [testObject id], [testObject name], [testObject email], [testObject createdDate]);

    }

}

The problem is that the above function deletes the existing record in the store, however, it fails to add the new entity that replaces it. Can someone show me how to correct this?

Thanks in advance to all who reply.

You are not calling save method on managed object context. Call save method on managedObjectContext in which you are creating new object. [managedObjectContext save:nil];

Recmonded way is. First fetch object depending on number, and delete it. After that create managed object. At the end call Save on context.

Hello, buddy!

责编内容by:Hello, buddy!阅读原文】。感谢您的支持!

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