I have a object graph which is defined by hibernate

node -> node ( many-to-many )

I have set the children with update cascade behaviour. The hibernate did the job prefectly. I can update a node and its auto update any change in its children.

But there is problem when I build a UI ( Java standalone client by SWT ) , call EJB and EJB call hiberante.

The problem is when hibernate update the node ( which is loaded from hibernate) , it will actully make some change on the object itself. In normal case, java 's object is pass-by-reference, that's fine. I use the updated node and do other things. Yet, during EJB calls are pass-by-value. The updated object cannot be passed back to the client whiich lead to problem.

An Example ( copy-and-paste button mechanism )

1) UI load the NodeA from EJB/hibernate
2) Press copy button, a reference is point one of the child in NodeA
3) Press paste button, the reference is added to somwhere
4) Press save, call EJB and hibernate save the record
( Up to above working fine )
5) Press paste again, the reference is added to somewhere ( currently the UI holding the node which passed to EJB, since EJB cannot pass-by-reference, its state does not change. ie. the old one )
6) Press save, call EJB and hibernate save the record. This will generally getting error ( either update incorrectly or generating error message.

Simple Test programme reproduced the problems

The error could be an exception or incorrect update. I would like to know is there better way to solve this ?

Make your bean return the saved/updated object.
i.e
r1 = bean.updateNode(r1)

--steve p.

This would not work in some case. For example, in the copy and paste example. The CopiedNode (r2) which has a reference to the "old" node child. Using will let the reference of r1 up-to-date. but the CopiedNode (r2) still using the old reference. since update(r1) will updated r2 too.

Does anyone have the same problem ? Any suggestion for the design ?