--- On Fri, 9/5/08, Michael Zimmermann <list@incunabulum.de> wrote:

  

rule "MyRule"
when
  book(year==myYear, author==myAuthor ...)
then
  ....

This works only if all properties myYear, myAuthor ... are
present. If one is undefined, the rule does not match.
    

You could have a function that returns true if the properties match or the property is null:

boolean matchesOrNull(Object o, Object p) {
  return p == null ? true : ( o == null ? true : o.equals(p) );
}

Call it using eval in the conditions.

Maybe if it's useful enough an operator could be added to Drools that does the same thing.  "~=" maybe?

GreG




      
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