Thanks for your time and answers, and sorry for the incomplete information.

There is a 1:1 relationship between EvemetierCalculDHF and EvemetierData objects. The reason for the EvemetierCalculDHF is that we want the EvemetierData structure to be independent from the rules, and therefore needed a declared fact (EvemetierCalculDHF) to type safely store some information. Ideally, we would like to add a trait to the EvemetierData instance, but is it possible on externally managed beans ?

=> The $evCalcDHF.evemetier returns a single object (and Drools correctly sees it a a single value and uses this value for the $obj). We could have written $obj:EvemetierData(this==$evCalcDHF.evemetier) but this created extra Tuples we want to avoid. And each time the EvemetierData is updated so is the EvemetierCalculDHF ; therefore the modification propagation still works despite the from. A binding variable would (correct me if I'm wrong) have done the same thing but in a possibly clearer way.

The "null wrapping" is mostly historical and will be changed to an Option in a near future. We functionally want that null + null = null and that 0+null=0. Similarly null/any should return null. But this is not related to this "too many RightTuple" problem, sorry I did not clean up the rule before sending it over.

I did not quite understand your last paragraph on a "representative". Do you have an example I could study ?

In a more general way, if I have a LHS with the following conditions:

$x: A(someConditions)

accumulate ($y:A(someField==$x.somefield); ....)

It seems that the Drools engine will create one RightTuple per instance of A (and per rule with a similar accumulate), even if no instance of A matches the someConditions.

If I have many instances of A in the WM, is there a way to prevent Drools to create the RightTuples for $y until it has found a valid $x, and therefore create RightTuples only for the A matching someField ? I could use a "from" in the accumulate, but then the engine will not see updates on $y instances and won't recalculate the accumulate.

Regards,

Benoît