[rules-users] [droolsflow] JPAKnowledgeService - how do you reload a Session with Processes?

[Bill Tarr]

Well, it sounds like my idea of a persisted Session might be different from what you have in mind.  
I have been thinking of Sessions as containers for a bunch of associated processes.

Let me ask this first: 

What is the purpose of persisting the SessionInfo @Entity?  

It has lost it's processes, what useful information does it have?  Why not just create a new Session and use it to open your processes?

I do recognize the need to maintain a list of processes associated any given domain objects (which for me are Claims.)

Let me lay out the system and use case, and my proposed solution, and you can tell me if I'm barking up the wrong tree.

MODEL
1. I have a *Claim* process
2. has 1..n of subflows in a ForEach representing documents
3. has 1 supporting subflows each for - Creation, Benefits, Subrogation

WORKFLOW
1. Each Claim (and subflows) interacts with several users
2. Long periods of time between user interaction (waiting for extenal stuff)

DESIGN IDEA
1. Create sessions and processes with JPAKnowledgeService on Claim create
2. Have Events as blocking points in the flows, persist - await User interaction
3. Store Session ID in Claim domain object (i.e. Claim#1002 is Drools Flow Session#879)
4. Events from User, reload session, **route Event to appropriate workflow**

USE CASE
1. Receive Event in Document #2 of 2
2. All Doc Process are now complete, return to Claim Process
3. Claim Process continues, enters Benefits Process

So, during one Event, Drools has closed a Process, returned to the parent Process, then opened a new Process as a subflow.  

If the reloaded Session knew all the processes associated with my Claim, I could handle events coming in easily.

Look at the session, find the active subflow, pass in the event.  Otherwise I must track all subflows.

Anyway, any help you can provide in helping me understand how to use the persistence model better is greatly appreaciated.

Bill



----- Original Message ----
From: Kris Verlaenen <kris.verlaenen at cs.kuleuven.be>
To: Rules Users List <rules-users at lists.jboss.org>; Bill Tarr <javatestcase at yahoo.com>
Sent: Thu, October 22, 2009 6:19:30 PM
Subject: Re: [rules-users] [droolsflow] JPAKnowledgeService - how do you reload a Session with Processes?

The getProcessInstances() method returns all process instances that are
currently loaded into the engine.  When using persistence, we
deliberately made that method to NOT fetch all active process instances
(as this could be thousands and that would impact performance).  So if
you use persistence, you will always get an empty list as the process
instances are not kept in memory but stored in the database.  But don't
worry, the engine will know when to reload process instances, you
shouldn't take care of that yourself.

Could you explain the use case you are trying to support in a little
more detail?  In general, I think you should be using a history log for
this, where you can query the active instances, the completed ones, what
happened, etc.

Kris

Quoting Bill Tarr <javatestcase at yahoo.com>:

> How do I FULLY reload my session with JPAKnowledgeService? 
> Specifically, shouldn't my session still know it's processes after
> reloading?
> 
> I'm using JPAKnowledgeService to persist my sessions and processes,
> after running, I have the following DB rows:
>    
>    SessionInfo - 1
>    ProcessInstanceInfo - 3 (1 ClaimFlow, and 2 subflow DocFlows)
> 
> I get a session properly with loadStatefulKnowledgeSession: 
> 
>    StatefulKnowledgeSession session =
> JPAKnowledgeService.loadStatefulKnowledgeSession( 1, knowledgeBase,
> null, env );
> 
> but this statement returns an empty collection:
> 
>    Collection<ProcessInstance> instanceCollection =
> session.getProcessInstances();
> 
> There is no key link between @Entity SessionInfo and
> ProcessInstanceInfo, so that result makes sense.... but shouldn't
> restoring the session restore the links to the active process within
> that session?
> 
> I can get the processes by id, but I'm not sure grabbing a subflow
> works in this example, I really want the session:
> 
>     ProcessInstance processClm = session.getProcessInstance(1);
> 
> Is there actually some other way to retrieve the processes from
> reloaded session?
> 
> As always, thanks for the help!
> 
> Bill
> 
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