I will explain why it happens and we can discuss how to improve that (at least improving the error message).

All temporal operators work when used against either an event, a date attribute or a long attribute (interpreted as a timestamp).

Wrapper( $eventA : foo )
$eventB : Bar( this after[0ms,1h] $eventA )

The engine has no idea that $eventA is an event in the working memory. From the engine's point of view, it is just a "foo" attribute from the Wrapper fact. So it checks if event A is a Date (nope), a long (nope) and finally tries to use it as an event raising the exception you see.

On your last example:

$eventA : Foo( this == $foo )

$eventA is an event in the working memory with all the internal metadata required to handle events. So, in this case, the engine knows how to deal with it.

Suggestions on how to improve that are welcome.

2010/8/13 Wolfgang Laun <wolfgang.laun@gmail.com>

According to the Fusion manual, "after" is used like this:

   $eventA : Foo(...)
   $eventB : Bar( this after[0ms,1h] $eventA )

provided Foo and Bar have @role(event).

This works.

But, given a class Wrapper( Foo foo ), the pattern combination
   Wrapper( $eventA : foo )
   $eventB : Bar( this after[0ms,1h] $eventA )
results in a class cast exception at runtime, telling me that a Foo cannot be cast to a org.drools.common.EventFactHandle.

Working around this by doing
Wrapper( $foo: foo )
$eventA : Foo( this == $foo )
$eventB : Bar( this after[0ms,1h] $eventA )

solves the problem, but is this really necessary and intentional? (The documentation doesn't even hint at such a restriction.)

-W

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Edson Tirelli
JBoss Drools Core Development
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