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From "Craig Russell (JIRA)" <j...@apache.org>
Subject [jira] Commented: (OPENJPA-968) Change in default detach() behavior for JPA 2.0
Date Mon, 09 Mar 2009 16:16:50 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-968?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12680187#action_12680187
] 

Craig Russell commented on OPENJPA-968:
---------------------------------------

I'd suggest that OpenJPA implement both detach() according to the JPA rules and rename the
original OpenJPA detach() to detachCopy(). Preserve the original rules for detachCopy and
for detach, follow whatever rules the JPA expert group decides on.

We can do this incompatible change with a major version, so it's unfortunate but not a disaster.
Users who fail to read the release notes will discover that their applications don't compile
and don't run, so it's not a silent failure.

Note that in JDO, the explicit detach method is named detachCopy, which has the same semantics
as OpenJPA detach. The decision was made to make it explicit that the detachCopy method creates
a copy of the instance in the context and leaves the original instance intact.

By the way, there was a lot of discussion in the JDO expert group about whether explicit detach
should make a copy or not, and it was pretty clear at the end that detach in place is tricky,
if not dangerous. 



> Change in default detach() behavior for JPA 2.0
> -----------------------------------------------
>
>                 Key: OPENJPA-968
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-968
>             Project: OpenJPA
>          Issue Type: Improvement
>          Components: kernel
>    Affects Versions: 2.0.0-M1, 2.0.0
>            Reporter: Pinaki Poddar
>            Assignee: Pinaki Poddar
>             Fix For: 2.0.0-M1, 2.0.0
>
>
> JPA 2.0 specification has introduced a detach() method in EntityManager. OpenJPA already
has a detach() method prior to JPA 2.0. There are several major differences between the new
method introduced in JPA 2.0 spec versus existing OpenJPA detach method.
> 1. The method signatures are different
>        JPA 2.0:              void detach(Object entity);
>        OpenJPA 1.x :   <T> T detach(T entity);
> 2. This signature difference also points to a basic difference in behavior. OpenJPA detach()
creates a copy of the given input entity and returns it. While JPA 2.0 specifies in-place
detach and hence returns a void.
> 3. The other basic difference is OpenJPA detach does not remove the input entity from
the persistence context. While JPA 2.0 specifies that the input entity be removed from the
context.
> 4. OpenJPA detach flushes a dirty instance before detaching. This implicit flush behavior
can be configured but flushing is the default.
> 5. OpenJPA detach() provides several options on which related instances will become detached.
They are 'loaded', 'fetch-group' and 'all'. With 'loaded' being the default.
>     Whereas JPA 2.0 introduces a DEATCH  cascade type and specified that the relationships
that are cascaded with DETACH or ALL be traversed during detachment.
>    It is not clear from the spec, however,
>    a)  whether an unloaded relation which has DETACH cascade will get loaded as a side-effect
of detach(). 
>    b) whether a relation that is currently loaded but not cascaded for DETACH will be
included in the detached graph. 
>    If answer to (a) is no and answer to (b) is yes, (which the spec does seems to suggest)
then we can effectively continue with 'loaded' as the default behavior. 
> To accommodate these differences following actions are proposed:
> A1. Request JPA Spec committee to change the API method in JPA 2.0 to OpenJPA detach()
method signature. If that request is not met, then change OpenJPA API according to JPA 2.0
spec. It will break backward compatibility of OpenJPAEntityManager API. There seems to be
no way out.
> A2. The default behavior will change in the following way
>              a) the detach will be in-place
>              b) no implict flush of dirty instances
>              c) based on condition, how JPA 2.0 spec clarifies the DETACH cascade and
loaded fields for inclusion in the detached graph, change 'loaded' default to 'cascade' default.


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