I'm wondering what is the best way to delete a LineItem in the mapping example in section 19.3 of the documentation.

For example, if a customer wanted to remove a product from their order, I would assume you would simply say;

session.delete(order.LineItems[0])

But this does not seem to work, (LineItem is an unknown entity).

Since LineItem is a composite element of Order, you should simply remove the LineItem in question from the collection, then Update() the Order--or if the Order is already associated with the session, just Flush().

Its the simply part thats throwing me.

my map looks like this


I try to remove the item like so (the commented line works as expected)

The Remove() method fails. I assume the problem is that branch.LeafList doesn't have a BranchID, but leafBranch does.

Something is confused in there, mainly because I think you have oversimplified things. If your association object ("Leaf-Branch"?) has no other properties, there is no point, you should just use a many-to-many relation. I'm not sure if that is your situation, or you've just simplified away it's other properties for the sake of demonstration.

If the latter, then I wonder why the object is carrying a "BranchID" property. That shouldn't be at all. BranchID is the column in hte table that related the two, but object-wise the relation is shown by the Leaf-Branch's membership in LeafList, no more. The Remove failure might have something to do with the fact that the the Leaf-Branch that is passed to remove is a different instance (representing the same row) as the one in the LeafList. I don't know what "LeafList not having a BranchID" means; LeafList only has Leaf-Branches. Another problem: even if this does work, you might see some really bad performance: the bag might have to remove and then re-add all the list elements (see http://www.hibernate.org/hib_docs/nhibe ... ollections ).

If the former (you didn't oversimplify, and this is actually what you have) you'd be far better off using a <set> many-to-many.

Thanks for your help marcal; I really appreciate your time.

Your right, I have stripped out a lot for demonstration. (hence the bag vs list) But I don't really have any buisness rules yet (i'm still setting up the database); I've been trying to get a handle on hibernate, and have been doing a lot of expermentation.

I can see my mistake with BranchID, but I'm going around and around. What I really want to do is simply remove an item from a collection. My needs seem quite similar to the example in section 19.3 so I followed that mapping.

Going back to that example. How would one say; remove a link to a product from the order, given the product id.

if one were to say

How do I get a hold of the lineItem instance to remove.

I can iterate through the LineItems collection and check for


But I feel like I should be able to use the ORM to do this sort of thing, and query directly for the lineItem with a spacific product id. I'm I still missing something or is this the best way to get at the lineItem?