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

[CK]

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