CODEWITHSUNDEEP
iosobjective-ccore-datanspredicate
HurkNburkS
HurkNburkS

Reputation: 5510

How to fetch a single object from Coredata using a predicate

I am trying to fetch a single object from my coredatabase, however it keeps returning null. My method is based off another method which returns every value from the coredata object that I am accessing..

I have never tried this before and have tried reading apples documents but its just not making sense.. this is what my method looks like

- (NSMutableArray *)readSelectedInstall:(NSString *)projIDString {
    NSManagedObjectContext *context = [self managedObjectContext];

    if (context == nil) {
        NSLog(@"Nil");
    }
    else {


        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        NSEntityDescription *entity = [NSEntityDescription entityForName:@"InstallProject" inManagedObjectContext:context];
        [fetchRequest setEntity:entity];

        NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ProjID==%@", projIDString];
        [fetchRequest setPredicate:predicate];

        NSError *error;

        NSMutableArray *installProjectDictionaryArray = [[NSMutableArray alloc] init];


        NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
        for (InstallProject *installProj in fetchedObjects) {

            NSMutableDictionary *tempInstallProjectDictionaryArray = [[ NSMutableDictionary alloc] init];

            [tempInstallProjectDictionaryArray setObject:installProj.companyName forKey:@"CompanyName"];
            [tempInstallProjectDictionaryArray setObject:installProj.projNo forKey:@"ProjNo"];
            [tempInstallProjectDictionaryArray setObject:installProj.projID forKey:@"ProjID"];

            [installProjectDictionaryArray addObject:tempInstallProjectDictionaryArray];
        }

        return installProjectDictionaryArray;
    }
    return nil;
}

any help getting me to return a single item thats projID matches the projIDString would be greatly appreciated.

Upvotes: 13

Views: 37742

Answers (2)

JohnVanDijk
JohnVanDijk

Reputation: 3581

What about the fetchLimit on the fetchRequest You can set that to 1

The fetch limit specifies the maximum number of objects that a request should return when executed.

E.g. in Swift:

let fetchRequest = NSFetchRequest(entityName: "Cart")
fetchRequest.fetchLimit = 1
fetchRequest.sortDescriptors = [NSSortDescriptor(key: #keyPath(Cart.creationDate), ascending: true)]

Edit: The sortDescriptors are set only because I was using this fetchRequest with an NFRC, you can just execute the fetchRequest too:

do {
  let fetchRequest = NSFetchRequest(entityName: "Cart")
  fetchRequest.fetchLimit = 1
  fetchRequest.predicate = NSPredicate(format: "name == %@", mainCart)
  var objects: [Cart]
  try objects = mainMoc.execute(fetchRequest) as! [Cart]
} catch {
  
}

Upvotes: 16

karthika
karthika

Reputation: 4091

Import NSManagedObject(InstallProject) and fetch one object like this,

-(InstallProject *)readSelectedInstall:(NSString *)projIDString
{

    NSArray *fetchedObjects;
    NSManagedObjectContext *context = [self managedObjectContext];
    NSFetchRequest *fetch = [[NSFetchRequest alloc] init];
    NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"InstallProject"  inManagedObjectContext: context];
    [fetch setEntity:entityDescription];
    [fetch setPredicate:[NSPredicate predicateWithFormat:@"(ANY ProjID contains[cd] %@)",projIDString]];
    NSError * error = nil;
    fetchedObjects = [context executeFetchRequest:fetch error:&error];

    if([fetchedObjects count] == 1)
    return [fetchedObjects objectAtIndex:0];
    else
    return nil;  

}

Upvotes: 18

Related Questions