Re: NSBrowser, NSTreeController and Core Data

FROM : Mark .
DATE : Tue Oct 14 16:15:31 2008

On Oct 13, 2008, at 15:44, Quincey Morris wrote:

> Your relationship is from categories to subcategories (and inversely
> from categories to parent categories). So calling the relationship
> "id" makes no sense. IAC, to-many relationship names make more sense
> if they're plural ("categories" instead of "id", and "parentCategory"
> instead of "parentID").


But I'm going to need to know the id of the category the user ultimately
selects.  And, I'm reading it as one parentID to-many ids.

> If 'childNode' is of a Cocoa class like NSXMLNode, [childNode
> stringValue] is going to return the same value each time, which
> doesn't look like what you want. If you're trying to get to various
> XML nodes or attributes, you're going to have to do it a different
> way. (Or perhaps you've invented a class that returns different
> results each time.) This all suggests that you believe that the
> relationships are implemented by matching of (string) names. They're
> not. Relationships are object references. Core Data is an object
> graph, not a database.


I'm sorry.  I should have included the other code.  I realize that
relationships are object references.  I am handling it in a different way. 
I'm looping through the nodes.  Also, what I had as "childNode", is actually
"categoryChildNode".

// Get an enumerator that contains all the children of this one category
listed in the XML

NSEnumerator *categoryChildEnumerator = [[categoryNode children]
objectEnumerator];
NSXMLNode *categoryChildNode = nil;

while (categoryChildNode = [categoryChildEnumerator nextObject]) {

    NSString *categoryChildName = [categoryChildNode name];

    if ([categoryChildName isEqualToString:@"CategoryName"])
    {
        [category setValue:[categoryChildNode stringValue] forKey:@"name"];
    }
    else if ([categoryChildName isEqualToString:@"CategoryID"])
    {
        [category setValue:[childNode stringValue] forKey:@"id"];
    }
    else if ([categoryChildName isEqualToString:@"CategoryParentID"])
    {
        [category setValue:[childNode stringValue] forKey:@"parentID"];
    }


... and so on

}

All this works fine with core data and an NSTextView.

> When you create a category object, it's going to have no subcategories
> yet, so there's nothing to set for that relationship immediately. If
> it has a parent, you need to find the parent object (possibly via the
> name of the parent object, which is another subject), and set that
> object for the parent relationship. (The inverse will get set
> automatically.)


> The to-many relationship is a NSSet, so if you ever need to add or
> remove subcategories from an object directly, you would use NSSet
> accessors. You won't use [setValue:forKey:] for that.


Given the error I received, I guess this is really my main question then. 
How do I do this?  Do I need to create a custom managed object class?

Regards,
Mark.