问包含关系中的对象的NSFetchedResultsController

EN

Parent *theParent = ...;
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Child"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"parent = %@", theParent];
[request setPredicate:predicate];

Country *theCountry = ...;
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Street"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"city.country = %@", theCountry];
[request setPredicate:predicate];

    // assume to have a valid key path and object
    NSString *keyPath;
    NSManagedObject *myObject;

    NSArray *keys = [keyPath componentsSeparatedByString:@"."];
    NSEntityDescription *entity = myObject.entity;
    NSMutableArray *inverseKeys = [NSMutableArray arrayWithCapacity:keys.count];
    // for the predicate we will need to know if we're dealing with a to-many-relation
    BOOL isToMany = NO;
    for (NSString *key in keys) {
        NSRelationshipDescription *inverseRelation = [[[entity relationshipsByName] valueForKey:key] inverseRelationship];
        // to-many on multiple hops is not supported.
        if (isToMany) {
            NSLog(@"ERROR: Cannot create a valid inverse relation for: %@. Hint: to-many on multiple hops is not supported.", keyPath);
            return nil;
        }
        isToMany = inverseRelation.isToMany;
        NSString *inverseKey = [inverseRelation name];
        [inverseKeys insertObject:inverseKey atIndex:0];
    }
    NSString *inverseKeyPath = [inverseKeys componentsJoinedByString:@"."];
    // now I can construct the predicate
    if (isToMany) {
        predicate = [NSPredicate predicateWithFormat:@"ANY %K = %@", inverseKeyPath, self.dataObject];
    }
    else {
        predicate = [NSPredicate predicateWithFormat:@"%K = %@", inverseKeyPath, self.dataObject];
    }

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"city.country = '%@'", theCountry];