"When I refresh the list of groups from each server, I need to find a way to keep the list of messages in the groups the user has subscribed to.

This is not a problem. As I mentioned in my previous reply, there is no need for you to physically delete the object, instead

• You can either mark it as inactive,
• or move it to another collection, which contains all news groups that the user once subscribed, but no longer exists.

Either way, you would still be able to preserve the messages in that group.

"Also, you tell me not to create a new list of objects, but then you tell me that copying message lists (and other properties) from the old list to the new list is a good solution. Which is it?"

Hm... That does not sound like what I suggested. But it could well be my fault, as I probably didn't explain myself well, or I probably didn't understand your entire situation well.

But is it not true, that the list of articles under an object can be re-hooked to a different object, without copying the entire list? If it is not, you have to look at this again.

Also, is it not true that, in a tree structure, when you reposition a node, you could choose to keep the entire subtree under it untouched (follows it to where it goes)? If that sounds like something you need, you may want to think about it.

Well, I may still not understand your entire situation well, but take my suggestions, if they fit in your situation, otherwise discard them or save them for next time. If we can discuss this face to face, it would surely be much easier for us to understand each other better, well...