On Aug 7, 2007, at 11:35 AM, Andy Jefferson wrote:
You could allow something of this form by imposing a restriction
that if an
object needs attaching, and that "AttachOnPersist" flag is set, and
the PM
already has a persistent object with that id then throw a
JDOUserException.
Clearly the primary use-case is where the user detaches a single
object, and
then wants to attach the same thing, so they typically never hit the
duplicate detached object issue.
You're right about the primary use case. With this restriction in
place, however, would I be able to do the following?
import static javax.jdo.JDOHelper.*;
assert pm.getAttachOnPersist() == true;
assert pm.getDetachAllOnCommit() == true;
// fetch a detched object
Query q = pm.newQuery(Foo.class);
q.setUnique(true);
Foo foo = (Foo) q.execute();
// my foo object is now detached-clean
assert isDetached(foo) && !isDirty(foo);
// make it dirty:
foo.setBar("bar");
// attach
pm.currentTransaction().begin();
pm.makePersistent(foo);
pm.currentTransaction().commit();
// should be transitioned back to detached-clean
assert isDetached(foo) && !isDirty(foo);
// dirty it once more
foo.addBaz("baz");
// and attach it a second time - wouldn't this cause the
JDOUserException you mention above? The pm is already managing (by
ID, I assume) this object, so how would it know the difference
between the application 'detaching and attaching two separate
instances of the same object' and simply 'attaching twice the same
instance of an object'? Hopefully I'm missing something, because I
like the proposed solution.
pm.currentTransaction().begin();
pm.makePersistent(foo);
pm.currentTransaction().commit();
// again, should now be detached-clean
assert isDetached(foo) && !isDirty(foo);
- Chris
