How to fetch only the first record in Core Data?

Question

I am using Core Data and I only want to fetch the first record in my dataset, is it possible?

Answer 1

You can use the setFetchLimit: method on NSFetchRequest to limit the number of records fetched. So if you only want the first record:

// Given some existing NSFetchRequest *request and NSManagedObjectContext *context: [request setFetchLimit:1]; NSError *error; NSArray *results = [context executeFetchRequest:request error:&error];

Note that the call to executeFetchRequest:error: will still return an NSArray; you still need to pull the first object off the array before you can work with it, even though it's an array of size 1.

Another, less efficient method: Depending on your store type, limiting the fetch may produce dramatic performance speedups. If it doesn't, however, or you're not that worried about performance, and you might use more data later, you can just pull the first object off the array ahead of time:

// Given some existing result NSArray *results: NSManagedObject *firstManagedObject = [results firstObject];

If you're sure that the array has an object in it, you can even get it into another array (for use in a UITableViewController, for example) by doing this:

// Again, with some NSArray *results: NSArray *singleObjectResult = [results subarrayWithRange:NSMakeRange(0, 1)];

Answer 2

Of course it partially depends on what you mean by the "first record". You may not only need to set the fetch limit to 1, but also to sort the results in the fetch.

For example, I have a bunch of User objects in my database, and I want to find the first one who created an account. (Assuming I already have the model for User, including one attribute named accountCreatedDate.)

NSEntityDescription *entity = [NSEntityDescription entityForName:@"User" inManagedObjectContext:managedObjectContext]; NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"accountCreatedDate" ascending:YES]; // ascending YES = start with earliest date  NSFetchRequest *request = [[NSFetchRequest alloc] init]; request.entity = entity; request.sortDescriptors = @[ sortDescriptor ]; request.fetchLimit = 1;  NSError *error; NSArray *fetchResults = [managedObjectContext executeFetchRequest:request error:&error];  User *result = fetchResults.firstObject; // nil on failure; check value of 'error' 

If you don't sort the results before limiting the fetch, there's no telling what results will be returned "first".