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

[Guto]

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
-- 
Guto Maia
CSM - SCJP- SCWCD - SCBCD - ZCE

 Chris,

When you use "==" in a DRL field constraint (not eval), drools always
translates it into an .equals() call.

Having said that, there might be other problems, since drools must rely on
object identity for some internal data structures... for instance, we use
IdentityMaps for mapping FactHandles and the actual fact objects, etc.

We would need to test this and see what can be done. Could you please open
a JIRA and attach a test case so that we can reproduce the problem?

Thanks, Edson

2009/4/26 CK <chri... at gmail.com>

Hi,

I'm testing out some simple codes using Hibernate and Drools 5 and I'm
hitting an issue with hibernate proxy objects.

With the newer version of hibernate, Javassist is used to proxy some
hibernate objects. By doing this, hibernate objects essentially cannot use
== comparisons, which is fine.

However, this is causing issue in equality checks within Drools 5 LHS
evaluations of hibernate persistent objects.

Let's say for example I have the following Hibernate objects:

class Parent { Child child; }

class Child { String name; }

normally, if you output Parent.child, it should be Child.class. But under
Hibernate, the child property in Parent may be proxied and enhanced with
Javassist, thus making Parent.child.class to be something like
"Child_$$_javassist_75".

Inside Drools, in the LHS:

when $child : Child() $parent : Parent(child == $child) then ... end

Assume that I have insert separate Child instances here that were
retrieved from an Hibernate query directly. Assume that I have also
inserted Parent instances that were retrieved from a separate query
without eager fetching. Given this particular case, the above rule would
not match even though it technically should. Under normal java code, using
equality, the parent's child is equal to the child.

According to MVEL language, which Drools LHS may not necessarily be using,
equality between two objects are compared using values. Not sure exactly
what that means.

Either way, this seems to be a rather unfortunate problem for using Drools
to work with Hibernate objects. Older hibernate versions didn't cause this
problem.

It seemed like jBPM had a similar problem according to the following doc:

http://www.jboss.org/community/docs/DOC-11169

Excerpt:

Object identity and object equality

MAKE SURE TO USE ALWAYS .equals AND NEVER == comparisons in the Java code.

Typically, in the PVM Java objects, we want to use the default object
identity as the object equality. But hibernate persistence breaks this
(even within the scope of one hibernate session) because of the proxies.
So we have to apply a trick in order to make the comparison between a
persistent object and its proxy return true. See jBPM 3 class EqualsUtil
for that trick.

So my question is whether Drools uses equality or identity when it comes
to comparing values in LHS constraints. Is there a way to get around this
issue?

-Chris

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-- Edson Tirelli JBoss Drools Core Development JBoss, a division of Red
Hat @ www.jboss.com

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