Hi Michael,
On Nov 2, 2005, at 7:13 AM, Michael Bouschen wrote:
Hi Craig,
+1!
The current spec has a section called "Attaching Instances" (at the
end of 12.6.8 Detaching and attaching instances). I assume this
section will then describe how to use makePersistent to attach
detached instances, correct?
That's correct. We also need to think about whether we change or keep
the name of the instance callbacks for attach. I think using the term
"attach" to describe the behavior of makePersistent applied to
detached instances is ok and we can keep the method names.
We also need to define what happens to transient fields of detached
instances when we attach them. Do they get copied or ignored? The
spec would lead me to believe that they are ignored. And if they are
ignored, is there a reason to optionally copy them with the
shallowCopyAll method?
Craig
A minor remark: I think the shallowCopy method taking an array of
objects should be called shallowCopyAll:
Object[] shallowCopyAll(Object[] original, boolean
copyTransientFields)
Regards Michael
Javadogs,
Please comment on this proposal.
There are so few differences between makePersistent and
attachCopy, it's confusing. The only significant differences
between the APIs is in the treatment of transient instances.
MakePersistent makes transient instances transition to persistent-
new; attachCopy copies transient instances.
The proposal is to remove attachCopy, change the signature of
makePersistent and makePersistentAll to return the instance(s),
and add a method to JDOHelper. The semantics of makePersistent
change slightly from the specification. Currently, detached
instances in the object graph cause an exception to be thrown.
With this change, detached instances are located in the persistent
cache and any dirty fields are applied to the persistent instance.
With this change, there is no standard way to attach the same
object graph to multiple persistence managers. So a method is
added to JDOHelper that copies a complete object graph so the
copies can be attached to multiple persistence managers.
Instead of:
Object[ ] attached1 = pm.attachCopy(graph);
Object[ ] attached2 = pm.attachCopy(graph);
use:
Object[ ] copies = JDOHelper.shallowCopy(graph, false);
Object[ ] attached1 = pm.makePersistentAll(copies);
Object[ ] attached2 = pm.makePersistentAll(copies);
The signatures of shallowCopy are:
Object shallowCopy(Object original, boolean copyTransientFields);
Collection shallowCopyAll(Collection original, boolean
copyTransientFields);
Object[ ] shallowCopy(Object[ ] original, boolean
copyTransientFields);
The copyTransientFields parameter specifies whether to copy the
transient fields of detached and transient instances. True
requires that the JDOHelper be given security privileges to allow
reflective copy. Non-binary-compatible implementations also
require security privileges. Binary-compatible implementations
will use the support for PersistenceCapable to copy the fields.
Support for deep copies is left to the implementation, as there is
no standard way to deep copy.
Craig
Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/
jdo
408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!
--
Michael Bouschen [EMAIL PROTECTED] Engineering GmbH
mailto:[EMAIL PROTECTED] http://www.tech.spree.de/
Tel.:++49/30/235 520-33 Buelowstr. 66
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