<div><br></div> Which version of Drools are you using?<div><br></div><div> Latest Drools versions changed the behavior of "from" to deal with it as you mentioned. So it will not raise ClassCastException. Instead:</div>
<div><br></div><div>$doc: Document(...) from $job.item // only matches if the returned item is a Document</div><div><br>$msg: Message(...) from $job.item // only matches if the returned item is a Message</div><div><br></div>
<div> I think 5.2 was the first version released with this change, but need to double check. For sure 5.3 works like that.</div><div><br></div><div> Edson</div><div><br></div><div><br><div class="gmail_quote">2011/10/11 hsherlock <span dir="ltr"><<a href="mailto:citadela@gmail.com">citadela@gmail.com</a>></span><br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">I have a following scenario in which a complex logic (distributed over<br>
multiple .DRL files) need to process incoming jobs as fast as possible. A<br>
job definition looks something like describing what to do (type), what to<br>
process (item) with some additional data supplied (args).<br>
<br>
enum JobType<br>
{<br>
VALIDATE,<br>
SEND<br>
}<br>
<br>
class Job<br>
{<br>
String type;<br>
Object item;<br>
Object[] args;<br>
}<br>
<br>
In order to implement the processing I need to put the business logic into<br>
rules which fire depending on the kind of processing requested and type of<br>
the item passed:<br>
<br>
rule "process [VALIDATION] on [Document]"<br>
when<br>
$job: Job(type==JobType.VALIDATE)<br>
$doc: Document(issued==true) from $job.item<br>
then<br>
insert(new DocumentAlreadyIssuedFact());<br>
end<br>
<br>
rule "process [SENDING] on [Message]"<br>
when<br>
$job: Job(type==JobType.SEND)<br>
$msg: Message() from $job.item<br>
then<br>
//do the sending<br>
end<br>
<br>
Unfortunately this does not work and results in ClassCastException being<br>
thrown, because it looks that Drools tries to cast any passed item to the<br>
class expected by the particular rule. In my opinion behaviour one can<br>
expect from Drools here is to first match the item class to the one expected<br>
by the rule and on success to perform the type casting.<br>
Is it a Drools bug or a missing feature?<br>
<br>
So after stidying the documention and example code I found only one way to<br>
workaround this – by using eval and instanceof which should have its<br>
performance implications due to extensive use of the eval.<br>
<br>
rule "process [VALIDATION] on [Message]"<br>
when<br>
$job: Job(type==”validate”)<br>
$msg: Message() from $job.item<br>
then<br>
//do the validation<br>
end<br>
<br>
rule "process [SENDING] on [Message]"<br>
when<br>
$job: Job(type==”send”)<br>
$msg: Message() from $job.item<br>
then<br>
//do the sending<br>
end<br>
<br>
Such an implementation works, but I see it as some form of workaround as my<br>
feeling is that it will not allow the optimizations of Drools to shine.<br>
<br>
Please recommend more effective and elegant way of implementing this.<br>
<br>
Thank you in advance<br>
<font color="#888888"><br>
--<br>
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<br>
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</font></blockquote></div><br><br clear="all"><div><br></div>-- <br> Edson Tirelli<br> JBoss Drools Core Development<br> JBoss by Red Hat @ <a href="http://www.jboss.com">www.jboss.com</a><br>
</div>