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iOS Core Data how to properly compare string text using predicates?
-(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;
}

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

if (!matches)
{
    NSLog(@"Error: couldn't execute fetch request %@", error);
}
else if([matches count] > 1) {
    NSLog(@"Error: More than one object for unique record");
    returnValue = YES;
} else if ([matches count] == 0) {
    NSLog(@"couldn't match objects");
    returnValue = NO;
} else {
    // [matches count] == 1
    NSLog(@"matched one object");
    returnValue = YES;
}