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From Craig L Russell <Craig.Russ...@Sun.COM>
Subject Re: Issue 135: Remove attachCopy from PersistenceManager
Date Wed, 02 Nov 2005 16:31:28 GMT
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?

> 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:Craig.Russell@sun.com
>> P.S. A good JDO? O, Gasp!
> -- 
> Michael Bouschen        Tech@Spree Engineering GmbH
> mailto:mbo.tech@spree.de    http://www.tech.spree.de/
> Tel.:++49/30/235 520-33        Buelowstr. 66
> Fax.:++49/30/2175 2012        D-10783 Berlin

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