Does merge() handle deletes?

[Landers, Richard]

Hello all,
 
I'm having trouble using EntityManger.merge() operation...
 
I have a entity A that holds a many-to-one reference to another, B. On
entity A, the relationship is annotated like this:
 
@ManyToOne(fetch=FetchType.EAGER, cascade=CascadeType.MERGE)
 
At a certain point in processing, I've got a detached instance of A
referencing an instance of B.
 
I want to dissociate A from any instance of B.  So I call:
 
    a.setB(null);
 
while A is detached, and then call:
 
    merge(a)
 
I thought the merge() operation would discover the change and update A
in the database, but it does not.
 
Is my mental model wrong?
 
Do I have to (or *can* I) mark A as "dirty" to get OpenJPA to notice it?
 
Thanks in advance,
 
  --Rich