[rules-users] Why Using "from" Always Return A New Fact?

[Greg Barton]

When you say "owning 100% of the language syntax" does that include the RHS?  Just curious.

GreG

On Jan 19, 2011, at 22:04, Edson Tirelli <ed.tirelli at gmail.com> wrote:

>   As of Drools 5.1.1, drools looks at the expression in "from" as a
> black box. Every time it is executed, drools creates a new fact handle
> to wrap the result(s). Since the lock and no-loop features are based
> on the fact handles, the sometimes undesired interaction occurs. We
> may be able to improve this in drools 6, when we will have the engine
> owning 100% of the language syntax, that will enable us to run better
> expression analisys than we can do today.
> 
>   Edson
> 
> Em quarta-feira, 19 de janeiro de 2011,
> hyjshanghai<hyjshanghai at gmail.com> escreveu:
>> 
>> You explanation is very reasonable:
>> the engine assumes anything within $p may be changed by modify($p), although
>> $p.address is not changed actually.
>> 
>> However, I tried these rules myself and both rules were fired. Why?
>> According to the document, only one of the rules should fire; the other's
>> activation should be cancelled because the engine assumes $p has changed,
>> which may mismatch the other rule, right?.
>> 
>> The following are the output and my rules. The only difference between my
>> rules and the document's is that my rules don't belong to any
>> ruleflow-group.
>> 
>> ==== Program Output of Inserting a "new Person()" and Firing All Rules.
>> BEGIN====
>> Rule 'Apply discount' fired. Person: Person{name[Tom],
>> address[Address{state[NC], city[Raleigh]}], region[null], discount[0.9]}
>> Rule 'Assign to sales region 1' fired. Person: Person{name[Tom],
>> address[Address{state[NC], city[Raleigh]}], region[sales region 1],
>> discount[0.9]}
>> ==== Program Output of Inserting a "new Person()" and Firing All Rules.
>> END====
>> 
>> ==== The Rules I Tested. BEGIN ====
>> package hello.rules
>> import java.util.*
>> import java.math.*
>> import hello.model.Address;
>> import hello.model.Person;
>> 
>> rule "Assign to sales region 1"
>> lock-on-active true
>> when
>>    $p : Person()
>>    $a : Address( state=="NC") from $p.address
>> then
>>    modify ($p) { setRegion("sales region 1") }
>>    System.out.println("Rule 'Assign to sales region 1' fired. Person:
>> "+$p);
>> end
>> 
>> rule "Apply discount"
>> lock-on-active true
>> when
>>    $p : Person()
>>    $a : Address( city=="Raleigh") from $p.address
>> then
>>    modify ($p) { setDiscount((float)0.9) }
>>    System.out.println("Rule 'Apply discount' fired. Person: "+$p);
>> end
>> ==== The Rules I Tested. END ====
>> 
>> ==== The Person and Address. BEGIN ====
>> public class Person
>> {
>>    private String name;
>>    private Address address;
>>    private String region;
>>    private float discount;
>>    public String getRegion() {
>>        return region;
>>    }
>>    public void setRegion(String region) {
>>        this.region = region;
>>    }
>>    public float getDiscount() {
>>        return discount;
>>    }
>>    public void setDiscount(float discount) {
>>        this.discount = discount;
>>    }
>> 
>>    public String getName() {
>>        return name;
>>    }
>>    public void setName(String name) {
>>        this.name = name;
>>    }
>>    public Address getAddress() {
>>        return address;
>>    }
>>    public void setAddress(Address address) {
>>        this.address = address;
>>    }
>>    @Override
>>    public String toString()
>>    {
>>        return String.format("Person{name[%s], address[%s], region[%s],
>> discount[%s]}",
>>                name, address.toString(), region, discount);
>>    }
>> }
>> 
>> public class Address
>> {
>>    private String state;
>>    private String city;
>>    public String getState() {
>>        return state;
>>    }
>>    public void setState(String state) {
>>        this.state = state;
>>    }
>>    public String getCity() {
>>        return city;
>>    }
>>    public void setCity(String city) {
>>        this.city = city;
>>    }
>> 
>>    @Override
>>    public String toString()
>>    {
>>        return String.format("Address{state[%s], city[%s]}", state, city);
>>    }
>> }
>> ==== The Person and Address END ====
>> --
>> View this message in context: http://drools-java-rules-engine.46999.n3.nabble.com/Why-Using-from-Always-Return-A-New-Fact-tp2286393p2292029.html
>> Sent from the Drools - User mailing list archive at Nabble.com.
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>> 
> 
> -- 
>  Edson Tirelli
>  JBoss Drools Core Development
>  JBoss by Red Hat @ www.jboss.com
> 
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