Remember that "collect" is a simplified form of "accumulate". So when you can't achieve what you want with collect, first thing you should look for is accumulate. $list : List() from accumulate( $foo : Foo( ) and not Bar( id == $foo.id ), collectList( $foo ) ) Please note that I changed your example making the constraint in Bar use "==" instead of "!=" because I think that is what you want. But if it is not, just use whatever expression you want. Also be aware that collect/accumulate are heavy CEs. Nesting multiple patterns inside accumulate is even heavier, so use it wisely. Hope it helps, Edson 2009/8/18 techy <techluver007(a)gmail.com&gt; -- Edson Tirelli JBoss Drools Core Development JBoss by Red Hat @ www.jboss.com