[rules-users] Can I capture the result of an RMI call within a pattern?

[Wolfgang Laun]

See below.

On 22 March 2012 17:25, lhorton <LHorton at abclegal.com> wrote:

> 5.2.0.Final
>
> consider this simplified example, which has RMI calls to a service to
> getLocation()
>
> rule "example"
> when
>   $p : Product( location != remoteService.getLocation("A") )
> then
>   $p.setLocation( remoteService.getLocation("A") );
> end
>
> the above rule calls the remote method twice, once in the LHS to compare to
> a current value, and again in the RHS to set the value.  I would like to
> capture the return value of the LHS call, to avoid making the call twice.
>  I
> haven't been able to figure out the syntax to do this within the pattern.
> Here's one example of what I have tried:
>
> rule "example"
> when
>   $p : Product( location != $loc : remoteService.getLocation("A") )
> then
>   $p.setLocation( $loc );
> end
>
> Does anyone know the correct syntax to accomplish this?  Or am I trying to
> do the impossible?
>

With a single rule: yes, I think. However:

   1. At the outset, you know that a comparison with Location A is required.
   2. If you have that firmly in your WM, you can compare and it's possible
   to use it on the RHS.

This is reflected by the following rules:

rule example1
when
     $p : Product( $mli: missingLocationId ) // that would be "A"
     not Location( id == $mli ) //  haven't RMI'd this yet
then
     Location loc = remoteService.getLocation( $mli );
     insert( loc );
end

rule example2
when
  $p : Product( $mli: missingLocationId )
  $loc: Location( id == $mli )
then
  $p.setLocation( $loc );
end

The idea here is to let a RHS execution intervene to do the RMI once.

-W



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