Hi,

I assume you mean Drools DRL (DSL is something different and none of your examples suggest use of this so far).

How about checking for the absence of the Double instead of it being null:-

when
    $product : Product( )
    not Double( ) from bookingService.getQty( $product )

I've not tried it personally.

With kind regards,

Mike

On 15 August 2012 19:54, Hendy Irawan <hendy@soluvas.com> wrote:
Thank you.

"this == null" is weird indeed in Java, but I honestly don't know how to
express this expression in Drools DSL.

A more realistic rule would be:

when
    $product : Product( )
    Double( this == null ) from bookingService.getQty( $product )

So what I want to do is detect when a method call returns null. The method
call can contain parameters but it can be a simple method like before.

How to do this?

Thank you.

Hendy



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