[rules-users] Hibernate proxy objects equality tests failing in Drools 5

CK chrisckc at gmail.com
Tue May 5 13:21:50 EDT 2009 

With the new hibernate jars and the migration to the new Javassist,  
what hibernate is essentially doing is dynamically generating  
hibernate proxy objects that should subclass the original file.   
Here's the interesting part.

In groovy, comparing two hibernate objects:

a.a == b.a

works fine when they are the same type of object.  Under groovy, "=="  
uses "equals()" to do the comparison.  That appears to work all good.   
However, taking these same two objects into Drools and comparing their  
subproperty when they are lazily loaded will cause the problems that  
a.a no longer equals to b.a.  Yet under groovy, it still says they are  
equal.

There could be one of 2-3 things that can be done to fix this, which I  
haven't entirely tried.

1) implement your own version of equals() and hashCode() and use the  
instanceOf() hibernate util method to do comparison.  Sadly, I have  
over 50 domains objects and I'm hoping not to have to implement all  
the methods.

2) do a eager fetch of the properties.  This is probably the best and  
easy way, but I am getting this working well under Grails/groovy.   
Somehow it's still fetching them as proxy objects, but just loaded.   
Either that or the eager fetching isn't even working (I've yet to  
fully test this yet with hibernate logging turned on to check).

3) use each domain's identity or some unique constraint to do the  
equality check.  This is my current "cheating" way of getting around  
the problem.  I simply use a.a.id == b.a.id.  However, this poses an  
additional complexity where I actually have to do null checks for the  
property.  Otherwise, I'd get NPEs all over the place.

At the end of the day, I don't see why Drools cannot see proxy objects  
as equal.  The only way I can think of is that there is some sort of  
direct object/class type check in Drools that's causing it not to  
realize that two objects are equal. But I could be wrong, and I hope  
I'm wrong. :)

-Chris

On May 4, 2009, at 1:29 PM, Guto wrote:

> Thanks Greg,
>
> But it´s not a lazy loading problem at all. I am not using any kind of
> lazy attribute inside the statefull drools session...
>
> Unfortunelly, i´ve just upgrade from drools 4GA to 5CR1 and the  
> problem
> persist. Now I will try to make CLONES of the objects the came from  
> the
> bank, just to see if that (temporary) solution works.
>
>>
>> Do you need the lazy loading functionality that proxies provide?   
>> It seems
>> to me that if you have an EJB call that's providing the objects  
>> loaded
>> from hibernate, that's probably not the case. (i.e. once the  
>> objects are
>> loaded and returned by the EJB method, the hibernate session may no  
>> longer
>> be available, so lazy loading could fail anyway.)  If you have  
>> access to
>> the hibernate mapping just set lazy="false" on your class mappings.
>>
>> Not to say that this use case shouldn't be addressed with drools,  
>> but if
>> you're under a deadline... :)
>>
>> --- On Mon, 5/4/09, Guto <guto at guto.net> wrote:
>>
>>> From: Guto <guto at guto.net>
>>> Subject: Re: [rules-users] Hibernate proxy objects equality tests
>>> failing   in Drools 5
>>> To: "Rules Users List" <rules-users at lists.jboss.org>
>>> Date: Monday, May 4, 2009, 2:42 PM
>>> Just now I notice one thing. The application that i am
>>> building is
>>> compleatly EJB centric. I have um EJB project that usually
>>> do all the
>>> database stuff, and another EJB project for the drools
>>> rules. Lets call
>>> them
>>> EJB-DATA and EJB-DROOLS. When the client calls for an
>>> specific data that
>>> must be threated thru the Drools rules it calls an
>>> Stateless method from
>>> EJB-DATA, inside the method, it gather the necessarie
>>> parameter
>>> information and them inside the EJB-DATA method it calls
>>> the EJB-DROOLS.
>>> (hoping not been confusing)
>>>
>>> (if you are using an fixed space font, here comes the
>>> sequence)
>>>
>>> Client --> EJB-DATA (gather information inside) -->
>>> EJB-DROOLS
>>>       <-- return to Client data from EJB-DROOLS<--
>>> return to EJB-DATA
>>>
>>> Now looking over my two projects, I notice that I make them
>>> apart so one
>>> could evolve with interfering the other.
>>>
>>> When I call EJB-DROOLS directly from an UNIT-TEST client
>>> with pojos
>>> parameters intantiated by the test, it pass.
>>>
>>> When I call EJB-DATA from an UNIT-TEST client (pojos
>>> created inside this),
>>> first i was getting an CORBA exception ´cause of a
>>> ClassNotFoundException
>>> for the hibernate PersistenceBag.
>>>
>>> That´s the way i figure out that my objects are bagged or
>>> proxied thru
>>> hibernate.
>>>
>>> I´ve tried to use the EntityManager.clear() (EJB3-JPA) to
>>> clean the pojos
>>> before send it and make them more like the ones from the
>>> first unit-test,
>>> but even so it´s not working.
>>>
>>> Then, possible solutions:
>>> 1) Make equality test works from objects that came from
>>> hibernate from jpa.
>>> 2) Kill the proxies and make them simple objects (not
>>> hibernate derivated).
>>> 3) don´t know, but i´m been realy in a deadline here.
>>>
>>>
>>> again
>>> thanks for anyone in advance !
>>>
>>> --
>>> Guto Maia
>>> Consultor de TI / Desenvolvedor
>>> CSM - SCJP- SCWCD - SCBCD - ZCE
>>>
>>>
>>>
>>>
>>>
>>>> In fact, i´m really using JPA with hibernate as an
>>> provider.
>>>>
>>>> Could you send me your hibernate config? I will
>>> compare some proprieties
>>>> of tyour hibernate.config with my persistence.xml.
>>>>
>>>> I plenty sure that the rule is ok, since it is working
>>> with the unit test.
>>>>
>>>> If you need any help to mimic what your using with
>>> JPA, just ask.
>>>>
>>>> Thanks anyway.
>>>>
>>>>
>>>>>
>>>>> I'm using non-proxied hibernate backed POJOs
>>> in drools with no problems.
>>>>> (THe pojos aer generaed by hbm2java.)  I'll
>>> try configuring for proxies
>>>>> to
>>>>> see what happens.
>>>>>
>>>>>
>>>>> --- On Mon, 5/4/09, Gustavo Maia Neto
>>> <guto at guto.net> wrote:
>>>>>
>>>>>> From: Gustavo Maia Neto <guto at guto.net>
>>>>>> Subject: Re: [rules-users] Hibernate proxy
>>> objects equality tests
>>>>>> failing in Drools 5
>>>>>> To: "Rules Users List"
>>> <rules-users at lists.jboss.org>
>>>>>> Date: Monday, May 4, 2009, 11:28 AM
>>>>>> on this afternoon I will migrate to Drools 5
>>> CR1,
>>>>>> unfortunelly i'm not
>>>>>> sure if it will solve my problem.
>>>>>>
>>>>>> Does anyone else uses Drools with objects that
>>> came from an
>>>>>> hibernate,
>>>>>> (proxies)?
>>>>>>
>>>>>> Also, i'm not using any proxy to fetch
>>> lazy data inside
>>>>>> my Drools
>>>>>> stateful session.
>>>>>>
>>>>>> thanks
>>>>>>
>>>>>> Guto escreveu:
>>>>>>> I was following that subject on markmail,
>>> and them
>>>>>> I've enterred the
>>>>>>> user-group (so subject and body are
>>> coppied from
>>>>>> them). I've got the
>>>>>>> exactly same problem. When I use the
>>> rules with
>>>>>> objects the came from the
>>>>>>> database (thru JPA hibernate provider),
>>> thouse rules
>>>>>> never match. When I
>>>>>>> do the same from Pojos hand made for unit
>>> test, it
>>>>>> work.
>>>>>>>
>>>>>>> I don't know what really happen, but
>>> i'm sure
>>>>>> that it is an equality test
>>>>>>> falling 'cause of the hibernate
>>> proxys.
>>>>>>>
>>>>>>> I don't get also any kind of error or
>>> exception,
>>>>>> since it ALL WORK. Just
>>>>>>> the rule isn't be acomplished.
>>>>>>>
>>>>>>> I'm using EJB3 + JPA (hibernate
>>> provider) and
>>>>>> Drools 4 GA;
>>>>>>>
>>>>>>> thanks in advance for any help
>>>>>>>
>>>>>>
>>>>>>
>>> _______________________________________________
>>>>>> rules-users mailing list
>>>>>> rules-users at lists.jboss.org
>>>>>>
>>> https://lists.jboss.org/mailman/listinfo/rules-users
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> rules-users mailing list
>>>>> rules-users at lists.jboss.org
>>>>>
>>> https://lists.jboss.org/mailman/listinfo/rules-users
>>>>>
>>>>
>>>>
>>>> --
>>>> Guto Maia
>>>> Consultor de TI / Desenvolvedor
>>>> CSM - SCJP- SCWCD - SCBCD - ZCE
>>>>
>>>> _______________________________________________
>>>> rules-users mailing list
>>>> rules-users at lists.jboss.org
>>>> https://lists.jboss.org/mailman/listinfo/rules-users
>>>>
>>>
>>>
>>>
>>>
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>>
>>
>>
>>
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>
>
> -- 
> Guto Maia
> Consultor de TI / Desenvolvedor
> CSM - SCJP- SCWCD - SCBCD - ZCE
>
> _______________________________________________
> rules-users mailing list
> rules-users at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users

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