Re-using RuleBook instance about rulebook

[Clayton7510]

Yes, you should be able to re-use a RuleBook by repeatedly calling run in the same thread.
Currently, RuleBook will chain the facts supplied to each rule on the run method.

[typhoon1978]

Ok, probably I'm using it in a wrong way but I try to explain as better as I know.

The problem I meet is this: I have a collection of rules that will evaluate a list of input objects, so my RuleBook represent a list of rules I want to "test" on all those objects that, according to tests, will be clustered setting a PeopleCluster enum value through the Consumer implementation.

If I instantiate it once, I have "repeated objects" in output not corresponding to their input objects.
If I instantiate it in the loop I have the correct behavior or better the behavior I expect.

And this is the example...

I have a testCases method which returns a list of NameValueReferableMap where MyBean is a simple bean with properties the rules will test through their predicates:

List<NameValueReferableMap<MyBean>> factsList = testCases();

All those beans are loaded from database and populated.

Then, I create my rules book EvaluationRuleBook which is an extension of CoRRuleBook, which contains a set of rules in defineRules method:

@Override
public void defineRules() {

	addRule(RuleBuilder.create().withFactType(MyBean.class).withResultType(MyResult.class)
				.when(ageLessThan(18)).then(unevaluated()).stop().build());
	addRule(RuleBuilder.create().withFactType(MyBean.class).withResultType(MyResult.class)
				.when(peopleFromUS()).then(evaluatedWith(true, true, PeopleCluster.F_1))
				.build());
         // and so on
}

Then I'm going to test this implementation:

RuleBook<MyResult> evaluationRuleBook = RuleBookBuilder.create(EvaluationRuleBook.class)
					.withResultType(MyResult.class)
					.withDefaultResult(new MyResult(null, false, false, null))
					.build();

factsList.forEach(x -> {
		evaluationRuleBook.run(x);
		evaluationRuleBook.getResult().ifPresent(result -> {
		MyResult ref = result.getValue().getRef();
		System.out.println(String.format("Item: %s, PeopleCluster: %s", ref.toString(), ref.getCluster().name()));
});

The unexpected is that in my loop I have the same number of input objects but "repeated": It seems return value is stored and for some reason not overwritten.

I expect that for every single object I "run" I have a return result referred to its input value.

On the contrary, if I instantiate the evaluationRuleBook inside the loop so that a new instance is built and used for each element of the factsList I have the expected results.

Is it my fault? Am I using it in a wrong way? Is the code sufficient to understand my problem?

Thanks in advance,
Alessandro.

[typhoon1978]

I repeated tests and understood that when rules predicates are not met, it returns the last not-null Result stored.

I expected a default Result like:

new MyResult(null, false, false, null)

as declared:

RuleBook<MyResult> evaluationRuleBook = RuleBookBuilder.create(EvaluationRuleBook.class)
					.withResultType(MyResult.class)
					.withDefaultResult(new MyResult(null, false, false, null))
					.build();

[typhoon1978]

Ok, I understood and now I need your help to understand if my concept of "default result" is the same of yours.

Method setDefaultResult is called inside withDefaultResult, so it's called once when we build the RuleBook and it stores the "default" return value in the same property used for the real return value.

When some rule is met and we have a real result, that default result is overwritten by the real return value and so we don't have a default result anymore.

What I needed was to store a default return value for the whole RealBook life-cycle and I thought that withDefaultResult method, called on the RealBook level, could be used for this purpose.

So the final question is... is the default result valid until we have a not-null result to return? or simply is it a bug?

Thanks in advance,
Alessandro.

[Clayton7510]

You are correct that withDefaultResult sets the initial result for the RuleBook by calling setDefaultResult. Within RuleBook, the Result object contains a reference to an object of the result type you specified. The withDefaultResult method initializes the Result object and allows that object to be chained across rules within a RuleBook. It is in effect an entity for that RuleBook (think EE's definition from DDD).

So, a default Result is never actually overwritten. However, the value of the Result object can be changed.

If you want to get the reference to the current result value, then modifying your example, you could do something like this.

public class EvaluationRuleBook extends CoRRuleBook<MyResult> {
    @Override
    public void defineRules() {
        addRule(RuleBuilder.create().withFactType(MyBean.class).withResultType(MyResult.class)
                .when(facts -> facts.getOne().getAge() <18) //assuming only one fact is used
                .then(f -> {})
                .stop()
                .build());
        addRule(RuleBuilder.create().withFactType(MyBean.class).withResultType(MyResult.class)
                .when(facts -> facts.getOne().isFromUSA()) //still assuming only one fact is used
                .then((facts, result) -> result.getValue().getPeopleInUSA().add(facts.getOne()))
                .build());
    }
}

public class MyBean {
    public MyBean(String name, int age, boolean american) {
        this.name = name;
        this.age = age;
        this.american = american;
    }

    private String name;
    private int age;
    private boolean american;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public boolean isFromUSA() {
        return american;
    }

    public void setFromUSA(boolean fromUSA) {
        american = fromUSA;
    }

    @Override
    public String toString() {
        return "MyBean{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", american=" + american +
                '}';
    }
}

Then you could run it using something like the following.

    public static void main(String args[]) {
        RuleBook<MyResult> evaluationRuleBook = RuleBookBuilder.create(EvaluationRuleBook.class)
                .withResultType(MyResult.class)
                .withDefaultResult(new MyResult())
                .build();

        MyBean[] beans = new MyBean[] {
                new MyBean("Herbert", 25, true),
                new MyBean("Edgar", 53, false),
                new MyBean("Joe", 17, true),
                new MyBean("Buck", 20, true)};

        for (MyBean bean : beans) {
            NameValueReferableMap<MyBean> facts = new FactMap<>();
            facts.setValue(bean.getName(), bean);

            evaluationRuleBook.run(facts);
        }

        evaluationRuleBook.getResult().ifPresent(result ->
            result.getValue().getPeopleInUSA().forEach(System.out::println));
    }

Using the above example, the MyBean instances for Herbert and Buck are in the rulebook's result upon completion of the loop and as a consequence they are printed to the console.

Personally, however, I would probably set different facts and run through the set of rules all at once instead of repeatedly calling your RuleBook subclass. Of course, I may have misinterpreted your exact application. :-)

Did that help to clarify?