Hi Edson,

Thanks for the reply. I see your point, and yes it should probably remain how it is today. It would be nice though if the documentation said that it didn't check the types :-)

However in my case, it was only throwing ClassCastExceptions if I specifically added the "eval(x instanceof Bar)" check, although you say that it should be doing this anyway? Perhaps it only throws the ClassCastException when you try to access a property, i.e. "name == 'bob'".

Also thanks for your comment on that bug. Looks like I can finally migrate to 5.0!

Cheers
Jevon

2010/2/26 Edson Tirelli <ed.tirelli@gmail.com>

   Hi Jevon,

   That is a discussion we had for some time (whether "from" should check return type or not for matching purposes). The only reason it was not implemented so far is that it would possibly cause "silent failures". Example:

Person( name == "bob" ) from $people

    If $people returns an Alien() and the check is in place, the rule will not match and the user might not notice the reason, as the way it is today, it will raise a ClassCastException.

    Although, in my opinion, the advantages of the check surpass the "silent failure" problem and we should add this check, specially because sometimes you have a collection of objects that share a common superclass, but with different actual subclasses instances, and you want to operate only on a give subclass.

    Anyway, I will talk with Mark and possibly add this to Drools 5.1.

    Regarding your keyword usage issue, I added a comment to it:

https://jira.jboss.org/jira/browse/JBRULES-2218

    Regards,
      Edson

2010/2/24 Jevon Wright <jevon@jevon.org>
Hi,

I am using Drools 4.0.7, and I had a DRL rule similar to the following:

rule "..."
  when
    other : Foo( )
    x : Bar( ) from other.property

  then
    ...
end

An unexpected bug occured. In some situations, other.property would _not_ be of type Bar, yet Drools would still think that it was. As a result I was getting some unusual exceptions being thrown: "org.mvel.CompileException: unable to resolve property: ..."

If I changed the rule to:
    x : Bar( ) from other.property
    eval ( x instanceof Bar )

It would instead throw a ClassCastException (i.e. "Baz cannot be cast into Bar").

If, instead, I changed the rule to:
    x : Bar( other.property == x )

It would start working correctly, and 'x' would only be of type Bar.

Is this known behaviour? Is it expected? If so, I would appreciate it if the 4.0.7 documentation was updated to reflect that "from" actually ignores the return type of properties. It took me a couple of hours to detect and fix this bug.

I would try these rules in Drools 5.x, but I'm still waiting for the blocking JBRULES-2218 to be resolved.

Cheers
Jevon

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--
 Edson Tirelli
 JBoss Drools Core Development
 JBoss by Red Hat @ www.jboss.com

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