Re: [eclipselink-users] When are Entities Equal?

[Gordon Yorke <gordon.yorke@xxxxxxxxxx>]

Hello Tim,
  Yes, as long as you continue to work within the same EntityManager 
without clearing then only one instance of any object will exist within 
that EntityManager/persistence context.  em.find(Employee.class, 
managerId) == department.getManager().  Unless you are in an Application 
Server you control when the EntityManager is closed or cleared. 
Container managed transactional entity managers will get switched at the 
end of the transaction.  Once you call clear or act on a different 
EntityManager then the instances from the old EntityManager will not be 
the same instances as retrieved from the new EntityManager.
--Gordon

Tim Hollosy wrote:
> I've got an entity with a many to one, let's call it employees, with a
> department.
>
> So my employee entity has a Department field.
>
> If I'm in the same Entity Manager and I do a find on an Employee to
> get an instance of a specific Employee Entity, then later in the same
> EM I do a select all on departments, my list of departments now
> contains a reference to the same Department that my Employee entity
> references.
>
> This is really great for doing things like databinding on drop down
> lists, because I can bind the list of departments directly to the
> department on my employee entity.
>
> However, is this safe? Can I count on these being the _same_ entities;
> not just entities with the same field values all the time? What's
> eclipselink doing behind the scenes?
>
> Thanks,
> Tim
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