Cocoa iPhone Recursive Array

Question

Hey there,

I'm using core-data and I have an entity that has an attribute called SID and another called ParentSID.

I'm trying to create a method where I can pass a fetched object from the set and it will return the lineage of that object by checking the ParentSID of each ancestor.

If the ParentSID is > 0 it should loop recursively until it finds an ancestor with the ParentSID of 0. Each time it loops it should add the ancestor to a lineage array.

If the ParentSID is 0 then it is done and should return the lineage array.

Not sure if this makes any sense.

Thanks, Howie

Answer 1

Are SID and ParentSID relationships or attributes? The situation you're describing sounds like it makes much more sense to implement as a relationship. That way, you can get the parent object by doing this: [object valueForKey:@"parentSID"]. Otherwise, you would need to do a whole fetch request like this:

NSFetchRequest *parentFetchRequest = [[NSFetchRequest alloc] init];
[parentFetchRequest setEntity:[NSEntityDescription entityForName:@"SID" inManagedObjectContext:managedObjectContext];
[parentFetchRequest setPredicate:[NSPredicate predicateWithFormat:@"parentSID == %@", [object valueForKey:@"parentSID"]];
NSArray *parents = [managedObjectContext executeFetchRequest:parentFetchRequest error:nil];
[parentFetchRequest release];
if ([parents count] == 0) {
    // TODO: Handle this error
    return;
}

NSManagedObject *parentSID = [parents lastObject]; 
// Now, at long last, you have a reference to the parent object.

To answer your specific question, I wouldn't do this as a recursive method. You can easily do this iteratively. For example:

NSManagedObject *sid = // get the original object
NSMutableArray *lineage = [NSMutableArray array];
while (sid) {
    NSMutableObject *parent = // get the parent using one of the techniques above
    if (parent)
        [lineage addObject:parent];
    sid = parent;
}