[rules-users] drools dynamic LHS

[Ansgar Konermann]

Am 24.05.2011 21:17, schrieb marunam:
> Let's say, if the business
> want to modify the rules with more fact values, I want to be able to happen
> this dynamically rather than changing the code for fact values and adding it
> there. 
Smells like YAGNI and a lot of accidental complexity.

I'd code in DRL exactly what your business requires when it requires it,
and design my software process in a way that allows to release/deploy
the rules on the fly (which is actually quite easy thanks to support in
Drools). Think "release/deploy to production three times a day".

Exception to this rule of thumb might be if you want to re-use the same
business rules for different customers but with different age limits,
like maybe in a multi-tenant application. But that's a different story.
In this case, you could define "configuration facts" which have to be
defined for each tenant, and which are used in the actual rules like so:

customer-a-configuration.drl:
rule "Configure age threshold"
when # fire always
then
  insertLogical(new AgeThreshold(24));
end

customer-b-configuration.drl:
rule "Configure age threshold"
when # fire always
then
  insertLogical(new AgeThreshold(27));
end

common-rules.drl:
rule "Check age threshold"
when
  AgeThreshold( $threshold: threshold )
  Person( age > $threshold )
then
  // do something
end


Best regards
Ansgar