Change in default detach() behavior for JPA 2.0
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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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