Apple introduced ordered to-many-relationships in Core Data in Lion. I created an entity named TreeNode with an 1:1-object-relation, a 1:1-parent-relation and an ordered to-many-relationship children.
Then I have an NSTreeController with the children key path set to TreeNode.children. Running the application only shows first level elements. So children is not working. Since children is an ordered to-many-relationship, the corresponding class has an NSOrderedSet children. I added a custom method
- (NSArray *) childrenArray {
return [children array];
}
to TreeNode which works. I could not find any documentation concerning that topic. Is it really the way to go when binding NSTreeController to an ordered to-many-relationship? Thanks in advance.
It seems that Apple gave us ordered sets for Core Data but forgot to upgrade its binding controllers. One year later after your question, the problem is still there.
Have a look at:
https://github.com/robertjpayne/DDOutlineView
Moral of the story. Be careful when using ordered relationships, try to do your own implementation until Apple fully implements that feature
来源：https://stackoverflow.com/questions/7039165/how-to-bind-nstreecontrollers-children-to-core-data-ordered-to-many-relationshi