[rules-users] Problem with JPA session persistence in Drools Flow (5.0.1)

[Alan.Gairey at tessella.com]

I'm currently using Drools Flow with JPA session persistence enabled as 
described in section 5.1 of the User Guide.
As a process executes, session information is saved to the H2 database 
correctly.
The problem comes if a process only executes part way through, and I then 
try to finish the process by recreating a session using the code:

// recreate the session from database using the sessionId
ksession = JPAKnowledgeService.loadStatefulKnowledgeSession( sessionId, 
kbase, null, env );
This gives me a NullPointerException.
Having looked into the Drools Flow source code, I think the problem is in 
the class 
drools-persistence-jpa\src\main\java\org\drools\persistence\session\SingleSessionCommandService.java.
The 4th constructor of this class is called as part of the loading of a 
knowledge session from the H2 database; this in turn leads to the 
afterCompletion method of the inner class SynchronizationImpl being 
called. The final two lines of this method are:

((JPAProcessInstanceManager) ((ReteooWorkingMemory) 
session).getProcessInstanceManager()).clearProcessInstances();
((JPAWorkItemManager) ((ReteooWorkingMemory) 
session).getWorkItemManager()).clearWorkItems();
However, when called via the route described above, the session member 
variable of SingleSessionCommandService has not been set, thus causing the 
NullPointerException.
(Interestingly, running the unit tests for drools-persistence-jpa does 
result in the NullPointerException being thrown multiple times, although 
the tests are still listed as having passed.)
I believe enclosing the above two lines as follows will fix the problem:

if (session != null) {
    ((JPAProcessInstanceManager) ((ReteooWorkingMemory) 
session).getProcessInstanceManager()).clearProcessInstances();
    ((JPAWorkItemManager) ((ReteooWorkingMemory) 
session).getWorkItemManager()).clearWorkItems();
}

Also, in the 4th constructor of SingleSessionCommandService, after the 
session has been set, the following line needs to be added to ensure the 
session id is the same as the session info id:

((ReteooStatefulSession) this.session).setId( this.sessionInfo.getId() );
(This line is present at the end of the 3rd constructor.)
It would be great if this fix could make it into the Drools 5.1 release.
Thanks.





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