Question

I am trying to fetch an entity from the core data depending on the attribute called “name”. Here is my code:

NSManagedObjectContext *context = [self managedObjectContext];



    NSEntityDescription *vegetable = [NSEntityDescription insertNewObjectForEntityForName:@"Vegetable" inManagedObjectContext:context];

    // get the vegetable using name

    NSFetchRequest *request = [[NSFetchRequest alloc] init];

    NSPredicate *predicate =
    [NSPredicate predicateWithFormat:@"name == %@", myGardenViewModel.vegetable.name];

    [request setEntity:vegetable];
    [request setPredicate:predicate];

    NSError *error; 

    NSArray *fetchedObjects = [self.managedObjectContext executeFetchRequest:request error:&error];

The last line throws the following exception:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Vegetable subentitiesByName]: unrecognized selector sent to instance 0x6bbcdd0'

any ideas?

Answer 1

The problem is the way you set up the entity property of your NSFetchRequest. With insertNewObjectForEntity: you are actually creating a new object to be inserted into the database later with [managedObjectContext save:&error];.

What you want to do is to just set the entity for your fetch request, rather than inserting a new object:

NSEntityDescription *vegetable = [NSEntityDescription entityForName:@"Location" 
   inManagedObjectContext:self.managedObjectContext];