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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