NSPredicate how to filter object fields - ios

Question

How do I filter an array of objects by a specific field?
My code:
NSMutableArray *inputArray = [[NSMutableArray alloc]init];
Person *person = [[Person alloc]init];
person.first_name = #"John";
[inputArray addObject: person];
person = [[Person alloc]init];
person.first_name = #"Jack";
[inputArray addObject: person];
NSString *expression = [NSString stringWithFormat:#"SUBQUERY(inputArray, $object, $object.first_name CONTAINS[c] J"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:expression];
NSMutableArray *filteredArray = [[inputArray filteredArrayUsingPredicate:predicate]mutableCopy];
NSLog(#"Count should be 2: %lu",(unsigned long)filteredArray.count);
This is the error I get:
'NSInvalidArgumentException', reason: 'Unable to parse the format string "SUBQUERY(inputArray, $object, $object.first_name CONTAINS[c] J"'
This is a basic example for testing. The real-case scenario is that I have an array of objects (Person or whatever) and I want to filter that array by certain fields within the objects ie first_name. As the user types we will filter a visual list based on what they type - so typing "J" would yield 2 results, but then when they type "Jo" only "John" appears on the list.
What am I doing wrong?
EDIT
Still doesn't seem to be working. Updated code:
DOVisitor *vi = [inputArray objectAtIndex:0];
NSLog(#"NAME: %#",vi.first_name);
NSPredicate *firstNamePredicate=[NSPredicate predicateWithFormat:#"first_name LIKE[cd] %#", #"Jo"];
NSPredicate *lastNamePredicate =[NSPredicate predicateWithFormat:#"last_name LIKE[cd] %#", #"Jo"];
NSPredicate *finalPredicate = [NSCompoundPredicate orPredicateWithSubpredicates : #[firstNamePredicate, lastNamePredicate]];
NSArray *filteredArray = [[inputArray filteredArrayUsingPredicate:finalPredicate]mutableCopy];
NSLog(#"Count should be 1: %d", [filteredArray count]);
I get an empty array back. However when I print the first object of the inputArray the console logs "John"
EDIT
Using CONTAINS instead of LIKE does the trick

Answer 1

You don't need a subquery for this, this is a very basic filter.
NSPredicate * predicate = [NSPredicate predicateWithFormat:#"first_name CONTAINS[cd] %#", #"j"];

Answer 2

Let us say you have Person object and you are trying to search for both firstName and lastName, then you can use:
NSPredicate *firstNamePredicate=[NSPredicate predicateWithFormat:#"firstName LIKE[cd] %#", #"Jo"];
NSPredicate *lastNamePredicate =[NSPredicate predicateWithFormat:#"lastName LIKE[cd] %#", #"Jo"];
NSPredicate *finalPredicate = [NSCompoundPredicate orPredicateWithSubpredicates : #[firstNamePredicate, lastNamePredicate]];
The final Predicate is generated by oring the previous predicates. So even if Jo is present in firstName or lastName, that Person object will pass the predicate test.
Edit:
Get filtered objects with above predicate
NSArray *filteredArray = [inputArray filteredArrayUsingPredicate:finalPredicate];