predicate is getting nil, nscoredata, objective

Question

What I am doing to fetch the data for core data is following

NSString *str;
NSPredicate *predicate;

switch (typeCube) {
    case NewCubes: {
        str = [NSString stringWithFormat:@"type == %d",NewCubes];
        break;
    }
    case AllCubes: {
        str = [NSString stringWithFormat:@"type != %d",CustomCubes];
        break;
    }
    case CustomCubes: {
        str = [NSString stringWithFormat:@"type == %d",CustomCubes];
        break;

    }
}

predicate = [NSPredicate predicateWithFormat:@"%@ AND (accounts.keyChainId == %@)", str, accountKeyChainId];

However, the result of predicate is nil. But the following works

predicate = [NSPredicate predicateWithFormat:@"(type == %d) AND (accounts.keyChainId == %@)", type, accountKeyChainId]; ( type is either NewCubes or AllCubes or CustomCubes)

Please help if you have any ideas. All comments are welcomed. Thanks

Answer 1

There is a class called NSCompoundPredicate which allows you to construct predicates with AND, OR and NOT operators. Here you need

[NSCompoundPredicate andPredicateWithSubpredicates:@[predicate1, predicate2, etc.]];

So the code will be --

NSPredicate *predicate1;
NSPredicate *predicate;

    switch (typeCube) {
        case NewCubes: {
            predicate1 = [NSPredicate predicateWithFormat:@"type == %d",NewCubes];
            break;
        }
        case AllCubes: {
            predicate1 = [NSPredicate predicateWithFormat:@"type != %d",CustomCubes];
            break;
        }
        case CustomCubes: {
            predicate1 = [NSPredicate predicateWithFormat:@"type == %d",CustomCubes];
            break;

        }
    }
    predicate = [NSPredicate predicateWithFormat:@"accounts.keyChainId == %@", accountKeyChainId];
    [NSCompoundPredicate andPredicateWithSubpredicates:@[predicate1, predicate]];

Read more about NSCompountPredicates here: http://nshipster.com/nspredicate/