[rules-users] Possible bug with isA operator

[Davide Sottara]

Thanks Mike, 
I have found and solved the problem, I'll commit the fix together with some
other improvements in the next few days. Can you open a JIRA for this?

The problem here is that, in order to be "traited", objects need a few
additional internal structures, hence the reason for the @Traitable
annotation. With declared beans, these structures are added automatically to
the class generated on the fly. With "legacy" (pojo) beans, that is
impossible - by convention we are not touching legacy classes - so a wrapper
is generated internally instead. 
When you applied the "isA" operator to a legacy object type, the operator
was looking for those additional structures. I have modified the operator to
go and look for the wrapper corresponding to an object, so calling isA on a
legacy bean WILL be possible, but discouraged.

Another option would be :

when
 $p : PojoFact( ... )
 [ not / exists ] Thing( core == $p )
then

All traits implement Thing, so this rule effectively looks for legacy
objects which have (not) been traited. You can use more specific types than
"Thing" if you want. With respect to "isA", which probably will be renamed
"hasType", this will also be triggered by more specific traits. Remember
that traits are interfaces, so inheritance is possible. The drawback here is
that your legacy bean must implement equals() ad hashCode() appropriately,
considering that an object might be compared not just with itself or objects
of the same class, but also with instances of proxy subclasses. 
For example, in your case you should write something like:

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if ( ! ( o instanceof PojoFact ) ) return false;
        PojoFact pojoFact = (PojoFact) o;
        if ( getId() != pojoFact.getId() ) return false;
        return true;
    }

    @Override
    public int hashCode() {
        return id;
    }

Feel free to ask more questions and report more bugs and suggestions ;) 
The code is very experimental and still work in progress, in time it will
come with better robustness and documentation
Best
Davide

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