Question

This is literally driving me nuts.

I have 2 entities that use NSStrings as unique attribute.

What is the correct way to create a predicate that compares NSStrings?

Currently I have:
[NSPredicate predicateWithFormat:@”unique= %@”, uniqueValue];

I have a feeling that this compares the pointer addresses, not actual string values, but I cannot confirm that. I need to return yes for an exact string match.

-(BOOL)uniqueEntityExistsWithEnityName:(NSString*)entityName UniqueKey:(NSString*) uniqueKey UniqueValue:(NSString*)uniqueValue SortAttribute:(NSString*)sortDescriptorAttribute ManagedObjectContext:(NSManagedObjectContext*) context;
{
    BOOL returnValue = NO;

    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:entityName];

//what is the correct predates to compare the text an string core data property against a passed in string?
    request.predicate = [NSPredicate predicateWithFormat:@"unique= %@", uniqueValue];

    NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:sortDescriptorAttribute ascending:YES];
    request.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];   

    NSError *error = nil;
    NSArray *matches = [context executeFetchRequest:request error:&error];
    if (!matches)
    {
         NSLog(@"Error: no object matches");
    }
    else if([matches count] > 1) {
        NSLog(@"Error: More than one object for unique record");
        returnValue = YES;

    } else if ([matches count] == 0) {
        returnValue = NO;
    } else {
        returnValue = YES;
    }

    return returnValue;
}

Answer 1

A single equal sign is not even a comparator in terms of coding.

I’m going to assume unique is an NSManagedObject attribute.

[NSPredicate predicateWithFormat:@"unique LIKE %@", uniqueValue];

Note that this is case-sensitive. If you want to make it insensitive, then you can put [c] after the LIKE.