Question

I am working on a simple comparison of two lists to see which items in an “evaluation” list are contained in a larger “target” list. I am getting the data on-the-fly- by parsing two CSV files and storing everything as strings. I successfully import the data into the data store and I can get a list of entities no problem

The problem comes when I actually do a search. Essentially, I am looking for short ISBNs in the form of 1234 from the evaluation list in the target list, which are in the form of 1234-5. The predicate I am using is I am using the CONTAINS comparison in the form of [NSString stringWithFormat:@"%@ CONTAINS %@", kOC_Target_PrintBookCode, evalIsbn]

The error I get is the following (grabbed by my NSLog)

NSInvalidArgumentException: Can't look for value (1494) in string (49885); value is not a string

I get the impression that even though the ISBN is being read from a NSString and the Core Data store has the data point spec’d as a String, that Core Data is still doing something in the background with the value for whatever reason it sees fit. Any ideas?

---

Here is the relevant process logic (though I use that term dubiously) code. Unless otherwise noted in the code, all values being manipulated and/or stored are NSString:

NSArray *evalBooks = [self getEntitiesByName:kOC_EntityName_EvalBook 
                             usingPredicateValue:[NSString stringWithFormat:@"%@ > \"\"", kOC_Eval_Bookcode] 
                       withSubstitutionVariables:nil 
                                         inModel:[self managedObjectModel]
                                      andContext:[self managedObjectContext] 
                                 sortByAttribute:nil];

    if ( ( !evalBooks ) || ( [evalBooks count] == 0 ) ) {
        // we have problem
        NSLog(@"( !evalBooks ) || ( [evalBooks count] == 0 )");
        return;
    }

    [evalBooks retain];

    int firstEvalBook = 0;
    int thisEvalBook = firstEvalBook;
    int lastEvalBook = [evalBooks count]; NSLog(@"lastEvalBook: %i", lastEvalBook);
    for (thisEvalBook = firstEvalBook; thisEvalBook < lastEvalBook; thisEvalBook++) {

        NSManagedObject *evalBook = [[evalBooks objectAtIndex:thisEvalBook] retain];

        NSString *rawIsbn = [[evalBook valueForKey:kOC_Eval_Bookcode] retain];
        NSString *isbnRoot = [[self getIsbnRootFromIsbn:rawIsbn] retain];
        // this is a custom method I created and use elsewhere without any issues.
        NSArray *foundBooks = [self getEntitiesByName:kOC_EntityName_TargetBook 
                                   usingPredicateValue:[NSString stringWithFormat:@"%@ CONTAINS %@", kOC_Target_PrintBookCode, isbnRoot]
                             withSubstitutionVariables:nil 
                                               inModel:[self managedObjectModel] 
                                            andContext:[self managedObjectContext] 
                                       sortByAttribute:kOC_Target_PrintBookCode];

        if ( foundBooks != nil ) {

            [foundBooks retain];
            NSLog(@"foundBooks: %lu", [foundBooks count]);

        } else {

        }

Answer 1

If you’re building your predicate as an NSString, I believe

[NSString stringWithFormat:@"%@ CONTAINS %@", kOC_Target_PrintBookCode, isbnRoot]

should actually be

[NSString stringWithFormat:@"%@ CONTAINS '%@'", kOC_Target_PrintBookCode, isbnRoot]

It seems that you’re confusing the way predicateWithFormat: works with the way stringWithFormat: works.