NSPredicate with subpredicates

Question

I have a Core Data object which contains some properties. 2 of those properties are:

• Country
• Place

What I want to achieve is that the user can select the countries which he wants to see, and also have the option to filter those countries on some places.

For instance:

The user wants to view only the objects from "USA" which have the place "New York" or "Chicago".

I've tried to do this with the following code:

NSMutableArray *subpredicates = [NSMutableArray array];
for (NSString *key in countryFilters) {
            NSPredicate *subpredicate = [NSPredicate predicateWithFormat:@"country contains[cd] %@", key];
            [subpredicates addObject:subpredicate];
}

for (NSString *key in placeFilters) {
            NSPredicate *subpredicate = [NSPredicate predicateWithFormat:@"place contains[cd] %@", key];
            [subpredicates addObject:subpredicate];
}

NSPredicate *filter = [NSCompoundPredicate orPredicateWithSubpredicates:subpredicates];

[self.fetchedResultsController.fetchRequest setPredicate:filter];

This works, but I also see objects which have a place with the same name but in another country... This is correct ofcourse, but I want to know how I can nest some NSPredicates (In this case: all or some countries, and from that result, only the ones with a specific place)

(Above is an example, my real objects contain other properties but the idea is the same. The only problem is that I cannot post the real object structure here for security purposes...)

Hope anyone can help..

Thanks in advance!

Answer 1

• Use p1 = [NSCompoundPredicate orPredicateWithSubpredicates:...] to create a predicate that filters the county (similar to what you already did, but only with the values from countryFilters.
• Use p2 = [NSCompoundPredicate orPredicateWithSubpredicates:...] to create another predicate that filters the place (now with the values from placeFilters).
• Use filter = [NSCompoundPredicate andPredicateWithSubpredicates:@[p1, p2]] to create the final predicate from the previous two predicates.