Exiting after executing a successful rule in Drools 6 - drools

I'm having an object as below:
class License{
private field1;
private field2;
private boolean active;
private String activeMessage;
private boolean processed = false;
//Getter and setter methods
}
What I'm trying to do is, based on the values of field1, and field2, I need to set the isActive flag and a corresponding message. However, if either the rule for field1 or field2 is fired, I need to stop the rules processing. That is, I need to execute only 1 successful rule.
I read on a post that doing ksession.fireAllRules(1) will solve this. But the fireAllRules() method is not available in Drools 6. I also tried putting a return; statement at the end of each rule. That didn't help me either.
Finally, I ended up adding an additional field to my object called processed. So whenever I execute any rule, I set the processed flag to true. And if the flag is already set, then I do not execute any rule. This is my rules file:
rule "Check field1"
when
$obj : License(getField1() == "abc" && isProcessed() == false)
then
System.out.println("isProcessed >>>>>> "+$obj.isProcessed());
$obj.setActive(true);
$order.setActiveMessage("...");
$order.setProcessed(true);
end
rule "Check field2"
when
$obj : License(getField2() == "def" && isProcessed() == false)
then
System.out.println("isProcessed >>>>>> "+$obj.isProcessed());
$obj.setActive(true);
$order.setActiveMessage("...");
$order.setProcessed(true);
end
However, I see that even now both my rules are being fired. When I try to print the value of isProcessed(), it says true, even though I enter the rule only if isProcessed() is false.
This is how I'm calling the drools engine:
kieService = KieServices.Factory.get();
kContainer = kieService.getKieClasspathContainer();
kSession = kContainer.newStatelessKieSession();
kSession.execute(licenseObj);
It is not just 2 rules, I have a lot of rules, so controlling the rules execution by changing the order of the rules in the drl file is not an option. What is happening here? How can I solve this problem? I am sort of new to Drools, so I might be missing something here.
Thanks.

Your question contains a number of errors.
It is definitely not true that fireAllRules has disappeared in Drools 6. You might have looked at the javadoc index, to find four (4!) overloaded versions of this method in package org.kie.api.runtime.rule in the interface StatefulRuleSession.
You might easily avoid the problem of firing just one out of two rules by combining the triggering constraint:
rule "Check field1 and field2"
when
$lic: License(getField1() == "abc" || getField2() == "def" )
//...
then
$lic.setXxx(...);
end
You complain that both of your rules fire in spite of setting the processed flag in the fact. Here you are missing a fundamental point (which is covered in the Drools reference manual), i.e., the necessity of notifying the Engine whenever you change fact data. You should have used modify on the right hand side of your rules.
But even that would not have been good enough. Whenever an update is made due to some properties, a constraint should be added to avoid running the update over and over again. You might have written:
rule "Check field1 and field2"
when
$lic: License(getField1() == "abc" || getField2() == "def",
! active )
//...
then
modify( $lic ){ setActive( true ) }
end
You might even write this in two distinct rules, one for each field, and only one of these rules will fire...

Related

Working with lists in Drools Rules Engine

I'm trying to work with lists in drools. I'm passing in a request which has a purchase list as part of it. I want to do several rules including checking if the size is correct, then if all elements are the same, if all purchases are authorized, ... I have the following code but I'm running into problems working with the list. Is this the right approach? Especially when checking for the size?
import com.rules.Purchase
import com.rules.PurchaseRequest
dialect "mvel"
global Boolean eligibleForRefund
rule "Check for list not equal to two elements" salience 10
when
PurchaseRequest(getPurchases != null, getPurchases.size() != 2)
then
drools.getKieRuntime().setGlobal("eligibleForRefund", false);
end
rule "Check for two purchases" salience 9
when:
$purchaseRequest: PurchaseRequest()
Number(intValue != 2) from accumulate(Purchase(getStatus() == "Approved") from $purchaseRequest.getPurchases(), count(1))
then
drools.getKieRuntime().setGlobal("eligibleForRefund", false);
end
rule "Check for the same purchases" salience 8
when:
$purchaseRequest: PurchaseRequest()
then
firstPurchase = $purchaseRequest.getPurchases().get(0).getCost();
hasAllElements = true;
for (Purchase purchase : $purchaseRequest.getPurchases()) {
if (purchase.getCost() != firstPurchase) {
hasAllElements = false;
}
}
drools.getKieRuntime().setGlobal("eligibleForRefund", hasAllElements);
end
Assuming that your class definition looks like this:
class PurchaseRequest {
private List<Purchase> purchases;
public List<Purchase> getPurchases() { return this.purchases; }
}
You should be pulling references out of the holder instead of constantly interacting with things via the getters. In other projects this helps with keep data consistent especially with shared resources. Recall that if you have a getter whose name matches the format getXyz, you can refer to it simply as xyz and drools will automagically map it to the getter function. This allows us to get the purchases via PurchaseRequest( $purchases: purchases ) since purchases will be mapped to getPurchases(). (Note that if purchases happened to be a public variable, it would have mapped to that first; but since it's private it falls back on the public getter that follows bean naming conventions.)
Second you use an accumulate in a very simple scenario where a collect would probably be more appropriate. Generally you'd use accumulate for more complicated "get things that look like this" sort of situations; but for simple matching, a collect works just as well.
The third rule needs the most work. You do not want to do this kind of business logic on the right hand side of your rule. There's a whole lot of ways you could go about checking that all the elements are the same -- if you've implemented equals/hashCode you could just shove everything into a set and confirm that the length of the set is still the length of the list; you could invert the rule to instead check for at least one item that's different; you could use accumulate or collect; ...
Finally --
Avoid saliences. They're bad design. Your rules should stand alone. You only need saliences here because your third rule sets both true and false. If instead you defaulted to true and then used the rules to override it to false, you could get away with having absolutely no saliences at all.
It's very unusual to use primitives for a global variable. I'm frankly not convinced that this will even work with a primitive. Globals work because the object is passed in by reference, and updated in the rules, and therefore the caller which retains the reference to the object will get the updated value. That doesn't work with primitives.
rule "Check for list not equal to two elements"
salience 1
when
PurchaseRequest($purchases: purchases != null)
List(size != 2) from $purchases
then
drools.getKieRuntime().setGlobal("eligibleForRefund", false);
end
rule "Check for two purchases"
salience 1
when:
PurchaseRequest( $purchases: purchases != null)
List( size != 2 ) from collect( Purchase(status == "Approved") from $purchases)
then
drools.getKieRuntime().setGlobal("eligibleForRefund", false);
end
// I've no idea what data type `getCost()` returns; I'm assuming "String"
rule "Check for the same purchases"
when:
PurchaseRequest($purchases: purchases != null)
// accumulate all of the costs into a set. if all costs are the same, set size = 1
$costs: Set() from accumulate( Purchase( $cost: cost ) from $purchases;
collectSet($cost))
then
drools.getKieRuntime().setGlobal("eligibleForRefund", $costs.size() == 1);
end

Get LHS in drools 6.5 to show in taskform

We have a situation where if rule fails, we need to show what condition is failed. For that I need to show LHS of a particular rule. How can we do that in drools6.5. I am using it in jbpm6.5. Please help.
import java.lang.Number;
rule "parent"
#author(rupesh)
dialect "mvel"
ruleflow-group "grp"
when
obj : Player( totalWinnings >= 10.0 )
then
System.out.println(drools.getRule().getMetaData());
System.out.println(drools.getRule().getMetaAttributes());
System.out.println(drools.getRule());
end
I am not able to get LHS in sysout.
I am assuming that you want to see the LHS values when a rule is not activated to understand why it happened.
To do that, create a function like this:
function boolean debug(double x) {
System.out.println("lhs_debug(): "+x);
return true;
}
and then modify the rule to use it, like this:
rule "parent"
when
obj : Player( debug(totalWinnings), totalWinnings >= 10.0 )
then
System.out.println("activated: "+obj.totalWinnings);
//do something
end
This will show you all attempts to activate the rule and will help you debug when it was not activated.
Please note that it will be very verbose and time consuming, so it should be removed after debugging.

Activate Rules on child objects in Drools

I have two Facts named OptionalCover and OptionalPremiumComponent and OptionalCover has a reference of OptionalPremiumComponent in it. So this is what I'm inserting into working memory.
private static OptionalCover getOptionalCover(Double sumAssured, Double premiumRate) {
OptionalPremiumComponent premiumComponent = new OptionalPremiumComponent();
premiumComponent.setSumAssured(sumAssured);
premiumComponent.setPremiumRate(premiumRate);
OptionalCover optionalCover = new OptionalCover();
optionalCover.setPremiumComponent(premiumComponent);
return optionalCover;
}
kieSession.insert(getOptionalCover(1000000.0, 0.02));
I have created the following rule in drools
import java.lang.Number;
rule "OptionalCoverCalculation"
dialect "java"
when
opc : OptionalPremiumComponent( sumAssured > 1I && sumAssured != null && premiumRate != null && premiumRate > 0.0 )
then
opc.setPremium( opc.getSumAssured() * 0.001 * opc.getPremiumRate() );
System.out.println("Here");
end
The problem is, the above rule is not being fired when I insert the parent object. Do I have to do anything else to enable this behaviour? Is it supported?
Thank you.
The Drools engine has no way of telling that your Cover contains a Component. (Well, it has, as it might use reflection - but where should it stop?)
So, you'll have to insert the OptionalPremiumComponent as well.
To reduce the amount of clutter in your code you might write a sorts of clever methods so that you can insert Cover and Component with a single call.
For instance, if you have many similar "contains" relationships and if you want to reason freely, you might implement s.th. like
interface FactContainer {
List<Object> factChildren(); -- return all contained fact objects
-- OR --
void insertAll( KieSession ks );
}
where factChildren would return a List with the premiumComponent or an empty List, or, alternatively, one method insertAll that handles everything internally.

Drools event lifecycle

I've had to create pairs of rules to retract my events. It seems they don't expire. I had wanted one-and-done events. You can see below, they use the default duration, zero.
So for example, if I exclude the retraction rules and then insert the RemoveConnectionEvent first and then insert the CreateConnectionEvent, the RemoveConnection rule will still fire. (Using an agenda listener in my unit tests)
My expectation of an event was that RemoveConnectionEvent would be ignored, it would not do anything if its conditions were not met immediately. I did not expect it to hang around and trigger the RemoveConnection rule once that rules conditions were met when the NewConnection rule responded to the CreateConnectionEvent.
To get my rules to behave as I expected, I created RetractedCreation, RetractedRemoval, and RetractedUpdate. This seems to be a hack. I am imagining a declared my events wrong.
Any ideas?
ps This was a pretty good Q&A but I am not using windows. It might infer that perhaps my hack is an 'explicit expiration policy'.
Test Event expiration in Drools Fusion CEPTest Event Expiration
Here is my rule.
package com.xxx
import com.xxx.ConnectedDevice
import com.xxx.RemoveConnectionEvent
import com.xxx.CreateConnectionEvent
import com.xxx.UpdateConnectionEvent
declare CreateConnectionEvent #role( event ) end
declare UpdateConnectionEvent #role( event ) end
declare RemoveConnectionEvent #role( event ) end
rule NewConnection
when
$connection : CreateConnectionEvent($newChannel : streamId)
not ConnectedDevice( streamId == $newChannel )
then
insert( new ConnectedDevice($newChannel) );
end
rule RetractedCreation
when
$creationEvent : CreateConnectionEvent($newChannel : streamId)
exists ConnectedDevice(streamId == $newChannel)
then
retract($creationEvent)
end
rule RemoveConnection
when
$remove : RemoveConnectionEvent($newChannel : streamId)
$connection : ConnectedDevice( streamId == $newChannel )
then
retract( $connection );
end
rule RetractedRemoval
when
$removalEvent : RemoveConnectionEvent($newChannel : streamId)
not ConnectedDevice(streamId == $newChannel)
then
retract($removalEvent)
end
rule UpdateConnection
when
$connectionUpdate : UpdateConnectionEvent($newChannel : streamId)
$connection : ConnectedDevice( streamId == $newChannel )
then
$connection.setLastMessage();
end
rule RetractedUpdate
when
$removalEvent : UpdateConnectionEvent($newChannel : streamId)
not ConnectedDevice(streamId == $newChannel)
then
retract($removalEvent)
end
This automatic expiry is a rather elusive feature. There's no concise definition when it'll work, and what needs to be done to make it work.
In your apparently simple case where you don't use temporal operators and expect that events are to be retracted after they have matched one rule I'd adopt the following strategy without wasting another thought on "inferred expiration" and "managed lifecycle".
Maybe you have a common (abstract) base class for your events; otherwise create a marker interface and attach it to all events. Let's call this type Event. Then, a single rule
rule "retract event"
salience -999999
when
$e: Event()
then
retract( $e );
end
will take care for all (Create, Update, Remove) events.
Edit You may also use the explicit setting for event expiry.
declare CreateConnectionEvent
#role( event )
#expires(0ms)
end
Make sure to use
KieBaseConfiguration config = ks.newKieBaseConfiguration();
config.setOption( EventProcessingOption.STREAM );
KieBase kieBase = kieContainer.newKieBase( config );
when creating the KieBase. I also recommend to "let the time pass", i.e., advance a pseudo clock or let the thread running a fireUntilHalt for a jiffy or two after fact insertion.

How to change default ConflictResolver

As stated in title I'd like to change conflict resolver in my Drools project. I found following snippet on this site
ConflictResolver[] conflictResolvers =
new ConflictResolver[] { SalienceConflictResolver.getInstance( ),
FifoConflictResolver.getInstance( ) };
RuleBase ruleBase = java.io.RuleBaseLoader( url, CompositeConflitResolver( conflictResolver));
However it lacks of information where to put it and what sholud be url parameter.
Thank you in advance for any help.
As the documentation says:
Drools 4.0 supported custom conflict resolution strategies; while this
capability still exists in Drools it has not yet been exposed to the
end user via knowledge-api in Drools 5.0.
http://docs.jboss.org/drools/release/5.2.0.Final/drools-expert-docs/html/ch04.html
So if you are using Drools 5+ you will not be able to change conflict resolver unless you do some reflection magic. The Conflict Resolver is settled inside the Agenda object of the StatefulKnowledgeSession object. You can see this by using debugger (it's the content of Agenda object):
To replace ConflictResolver, first you need instance of StatefulKnowledgeSession (which will be ksession in the following snippet). Then you need to extract some nested private fields and after that you can replace field value with instance of i.e RandomConflictResolver. Full code:
Agenda agenda = ksession.getAgenda();
Field agendaField = agenda.getClass().getDeclaredField("agenda");
agendaField.setAccessible(true);
Object agendaObject = agendaField.get(agenda);
Field mainField = agendaObject.getClass().getDeclaredField("main");
mainField.setAccessible(true);
Object mainObject = mainField.get(agendaObject);
Field queueField = mainObject.getClass().getDeclaredField("queue");
queueField.setAccessible(true);
Object queueObject = queueField.get(mainObject);
Field comparatorField = queueObject.getClass().getDeclaredField("comparator");
comparatorField.setAccessible(true);
Object comparator = comparatorField.get(queueObject);
ConflictResolver randomResolver = org.drools.conflict.RandomConflictResolver.getInstance();
comparatorField.set(queueObject, randomResolver);
Based on : documentation and debugger session.
To demonstrate that the order of firings does not affect the overall outcome I'd use an AgendaFilter. I'm sketching the outline using 6.x, but this API hasn't changed since 5.x.
KieBase kieBase = ...;
Collection<KiePackage> packages = kieBase.getKiePackages();
List<Rule> rules = new ArrayList<>();
for( KiePackage p: packages ){
rules.addAll( p.getRules() );
}
Now you have all the rules. Build this simple filter that accepts a single rule:
class Selector implements AgendaFilter {
List<Rule> rules;
int ruleIndex;
Selector( List<Rule> rules ){
this.rules = rules;
}
void setRuleIndex( int value ){ this.ruleIndex = value; }
int getRulesSize(){ return rules.size(); }
boolean accept(Match match){
return match.getRule().equals( rules.get( ruleIndex ) );
}
}
Instantiate:
Selector selector = newSelector( rules );
You can now execute all rules that are activated (but see below):
for( int i = 0; i < selector.getRulesSize(); ++i ){
int fired = kieSession.fireAllRules( selector, i );
}
Any other permutation of 0..size-1 may produce another sequence of firings. You may do this systematically for a small number of rules, or you may use some random permutations.
A more efficient test would keep track of the Match data passed to the filter in the first run and use only these for successive executions.
Caution The approach outlined so far does not consider changes in Working Memory. It would be possibe for rule n to become activated when some rule n+k is fired. If you do have changes of Working Memory, you will have to
do {
int sumf = 0;
for( int i : somePermutation ){
int fired = kieSession.fireAllRules( selector, i );
sumf += fired;
}
} while( sumf > 0 );
I have never done a test like this. It seems that getting the correct result by depending on the innate order of rule firings is extremely rare, in contrast to getting all sorts of wrong results from this order.
Note Other permutations of the rule firing order are possible by changing the order of rules in the DRL (or in their packages?) or by changing the order of fact insertions into working memory. For certain scenarios, even this may provide enough test cases for showing what you intend.