[rules-users] Drools - Query Problem

[Esteban Aliverti]

Hi,
What Wolfgang is trying to say about "inform" the Drools engine about the
update is that you need to use a modify statement in your RHS. Your rule
should look like this:

*rule* "for E band"
        lock-on-active true
        *when*
                r : Rating( rate == 1)
        *then*
                                modify(r){
                   setBand("EBand");
                                }
                System.out.println( "in E band" );
*end*

This is the way to inform Drools that your Fact is modified. But be careful,
because when you modify a Fact, all the rules are evaluated again because
the modification could activate another Rule. This will end in an infinite
loop (just like Wolfgang mentioned), the "for E band" rule will be executed
for ever. That's why you need to add the no-loop attribute (if the only rule
that modifies a Rating is "for E band") or lock-on-active (if more than one
rule could modify a Rating).

On Mon, Mar 29, 2010 at 7:20 AM, Wolfgang Laun <wolfgang.laun at gmail.com>wrote:

> You have to inform the Drools engine about the update done with
> r.setBand("..."), or else the query condition is still seeing the fact
> state at insert time.
>
> You may have to add the no-loop option to your rules.
>
> (Also, comments and actions disagree, e.g. "D Band" vs. "EBand")
>
> -W
>
> On 3/29/10, Nilima R <nilima.r at tcs.com> wrote:
> > Dear All,
> >
> > I have created simple rule file and created model in that rule file only
> >
> > package com.sample
> >
> > import java.lang.String;
> >
> > declare Rating
> > rate : int
> > band : String
> > name : String
> > end
> >
> > query "employee with band E"
> > ratg : Rating(band == "EBand")
> > end
> >
> > rule "for E band"
> >
> >         when
> >                 r : Rating( rate == 1)
> >         then
> >                 r.setBand("EBand");
> >                 System.out.println( "in E band" );
> >
> > end
> >
> > rule "for D band"
> >
> >         when
> >                 r : Rating( rate == 2)
> >         then
> >                 r.setBand("EBand");
> >                 System.out.println( "in E band" );
> >
> > end
> >
> > rule "for C band"
> >
> >         when
> >                 r : Rating( rate == 3)
> >         then
> >                 r.setBand("EBand");
> >                 System.out.println( "in E band" );
> >
> > end
> >
> > rule "for B band"
> >
> >         when
> >                 r : Rating( rate == 4)
> >         then
> >                 r.setBand("EBand");
> >                 System.out.println( "in E band" );
> >
> > end
> >
> >
> > At the end I want to know how many employees have got E band and so have
> > written query for it in the rule file .and obtained the query results as
> > below
> >
> >
> > FactType bandType = kbase.getFactType( "com.source", "Rating" );
> >                         QueryResults results = ksession.getQueryResults(
> > "employee with band E");
> >                         System.out.println( "we have " + results.size() +
> > "employee with band E" );
> >                         System.out.println( "employee with band E:" );
> >
> >                         for (Iterator i = results.iterator();
> > i.hasNext();) {
> >                             QueryResultsRow row =
> > (QueryResultsRow)i.next();
> >                             Object ratg = row.get("rating");
> >                             String name = (String) bandType.get( ratg,
> > "name" );
> >                             System.out.println(name);
> >                          }
> >
> >
> > But am getting the result of query as 0 records.
> >
> >
> > i am inserting objects one by one ( this for testing just purpose ) to
> > learn how query works.
> >
> >
> > Can someone plz point out what is wrong.Its Urgent ................
> >
> >
> > Thanks in advance.
> > Nilu
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Esteban Aliverti
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