Question

I am very new to the Core Data programming. I have a question to which I hope to get some clarification.

Supposing I have an NSManagedObject called Company, with the following attributes:

• companyName
• companyEmail
• companyPhoneNo
• companyUserName
• companyPassword

In this object the companyName attribute is indexed.

So, my question is, how can I make sure that there will be only entry with same companyName, companyEmail, companyPhoneNo, companyUserName and companyPassword?

Do I need to make a request to check if there are any records with the same attribute values or is a simple check with the object id sufficient?

Thanks.

Answer 1

Here’s an example may be helps:

NSError * error;
NSFetchRequest * fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:[NSEntityDescription entityForName:NSStringFromClass([self class])
                                    inManagedObjectContext:managedObjectContext]];
[fetchRequest setFetchLimit:1];

// check whether the entity exists or not
// set predicate as you want, here just use |companyName| as an example
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:@"companyName == %@", companyName]];

// if get a entity, that means exists, so fetch it.
if ([managedObjectContext countForFetchRequest:fetchRequest error:&error])
  entity = [[managedObjectContext executeFetchRequest:fetchRequest error:&error] lastObject];
// if not exists, just insert a new entity
else entity = [NSEntityDescription insertNewObjectForEntityForName:NSStringFromClass([self class])
                                            inManagedObjectContext:managedObjectContext];
[fetchRequest release];

// No matter it is new or not, just update data for |entity|
entity.companyName = companyName;
// ...

// save
if (! [managedObjectContext save:&error])
  NSLog(@"Couldn't save data to %@", NSStringFromClass([self class]));

Tip: countForFetchRequest:error: does not fetch entity actually, it just returns a number of entities that match the predicate you set before.