Question

I have some encrypted NSString store in a transformable field. I need to decrypt and list all value in alphabetical order.

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] 
                                    initWithKey:@"trans_word" 
                                    ascending:YES
                                    comparator:^NSComparisonResult(id obj1, id obj2) {
    NSString* s1 = [encryptObj decryptingfromValue:obj1]; 
    NSString* s2 = [encryptObj decryptingfromValue:obj2]; 
    NSLog(@"xxx");
    return [s1 compare:s2];
}];
NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];

It seems the block doesn’t performance. Could you give me any hints? Thanks!

Answer 1

On iOS and on OS X prior to 10.6 and when using SQLite-based stores, block predicates are not supported.

Special Considerations

In Mac OS X v10.6, Core Data supports this method in the in-memory and atomic stores, but not in the SQLite-based store. (Link)