So, I assume the fact that is not needed in the LHS is Income.
By inserting Income into Working Memory, you are subjecting it to rete
evaluation against the current knowledge tree. I consider the cost of each
operation. Insert is very costly, and insertLogical even more costly.
I don't know anything about how your data model is built, but based on this
very simple example, I would think you would be better off with a Global like
this:
Global Income income
Style 1: one rule for each scenario
rule "household income, single"
when
$p1 : Person()
not Relation(person1 == $p1, type == "spouse")
then
income = new Income($p1.getIncome());
end
rule "household income, married"
when
$p1 : Person()
Relation(person1 == $p1, type == "spouse", $p2: person2)
then
income = new Income($p1.getIncome() + $p2.getIncome());
end
Style 2: a single rule with a collection
rule "household income "
when
$p1 : Person()
$rels : List() from collect(Relation($p1 == person1, type ==
"spouse"))
then
income = new Income($p1.getIncome() + ($rels.size() == 0 ? 0 :
$rels.get(0).getPerson2().getIncome());
end
Then in code, you can get the Global value to determine what it got set to, if
you need outside of the Drools processing. All thread safety factors must be
considered in a multi-threaded environment. Global are not objects know to
rete, and therefore, use of them is very fast in the LHS. And the RHS is never
aware of changes to Globals (drools assumes them to be static values, that do
not change) so care must be taken if using them in the RHS of rules, which I
would advise against doing except for special cases where you know a change in
the global variable won't be a problem (such as this simple scenario where the
global is not used in the RHS at all).
-----Original Message-----
From: rules-users-boun...@lists.jboss.org
[mailto:rules-users-boun...@lists.jboss.org] On Behalf Of Christopher Dolan
Sent: Monday, April 23, 2012 1:01 PM
To: rules-users@lists.jboss.org
Subject: [rules-users] Best practice for 0..1 relations
What's the best way to encode a fact that's needed in the RHS but is not
important in the LHS?
Consider a contrived example of computing total household income for single or
married persons. I can think of two ways to encode this rule, but I don't like
either of them:
Style 1: one rule for each scenario
rule "household income, single"
when
$p1 : Person()
not Relation(person1 == $p1, type == "spouse")
then
insertLogical(new Income($p1.getIncome()));
end
rule "household income, married"
when
$p1 : Person()
Relation(person1 == $p1, type == "spouse", $p2: person2)
then
insertLogical(new Income($p1.getIncome() + $p2.getIncome()));
end
Style 2: a single rule with a collection
rule "household income "
when
$p1 : Person()
$rels : List() from collect(Relation($p1 == person1, type ==
"spouse"))
then
insertLogical(new Income($p1.getIncome() + ($rels.size() == 0 ? 0 :
$rels.get(0).getPerson2().getIncome()));
end
(please ignore the bug that the income may get inserted twice because people
are spouses of each other)
Style 1 is more verbose, but more straightforward: it's how I think of the
problem intuitively. Style 2 is much more compact, and is more maintainable if
I need to add more predicates or a more complicated RHS. But the idea of
needing a List when I know there will be exactly 0 or 1 related facts just
seems wrong.
I've searched for some LHS syntax that assigns a variable without participating
in boolean evaluation, but I've failed to find anything.
Chris
_______________________________________________
rules-users mailing list
rules-users@lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users
_______________________________________________
rules-users mailing list
rules-users@lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users
