Re: [rules-users] "from" keyword does not actually check types?

-----Original Message----- From: rules-users-bounces(a)lists.jboss.org [mailto:rules-users- bounces(a)lists.jboss.org] On Behalf Of Simon Thum Sent: 03 March 2010 11:08 To: Rules Users List Subject: Re: [rules-users] "from" keyword does not actually check types? Edson Tirelli wrote: > 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. FWIW, I'd appreciate both options being possible. Maybe an explicit qualification makes sense, like (subset|all)? from ... so you'd retain error checks where appropriate. > > 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(a)jevon.org&gt; > >> 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 >> >> _______________________________________________ >> rules-users mailing list >> rules-users(a)lists.jboss.org >> https://lists.jboss.org/mailman/listinfo/rules-users >> >> > > > > ------------------------------------------------------------------------ > > _______________________________________________ > rules-users mailing list > rules-users(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/rules-users _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users