Hi All,
Just wanted to share with you an easy mistake. This is done running
Drools 5.5.0.Final.
Imagine a fact
|Cheese (||
|| creationTick : double||
|| preservationTicks : double||
||)|
Then the following does not do what you expect:
|rule "dump old cheese"||
|| when||
|| $c : Cheese( $sbd : creationTick + preservationTicks )||
|| CurrentTime( tick >= $sbd )||
|| then||
|| System.out.println("||we have to dump "+$c);||
||end|
You would expect that $c is dumped when current time has passed
creationTick + preservationTicks. But no. The variable $sbd is bound to
creationTick /before/ the preservationTicks are added!! I must say that
I do not quite understand how ($sbd : creationTick) + preservationTicks
resolves to "true" to make the premise succeed... Maybe because it is != 0?
I found that it should be:
|rule "dump old cheese"||
|| when||
|| $c : Cheese( $sbd : (creationTick + preservationTicks) )||
|| CurrentTime( tick >= $sbd )||
|| then||
|| System.out.println("we have to dump "+$c);||
||end|
This makes sense. Now $sbd is bound to the result of the addition. But
it is an easy trap!!
Regards,
Willem
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