Writing method of then part in drools

1、 background

Here is an introduction to drools in then Part of it , And some built-in methods , such as insert/delete/modify wait . Also introduce rule Inheritance , And in when To realize if else if Wait for the operation .

2、 Supported methods

drools Some built-in methods are provided , These methods will modify drools Of The working memory in Fact The value of the object . This will result in pattern matching again .

2.1 insert Insert object into working memory

insert Is to insert objects into working memory , At the same time, it will lead to the re pattern matching of rules . At the same time, when the rules are not satisfied , Will not automatically delete .

2.1.1 demand

When there is a fire Fire when , Insert a... Into the working memory Alarm object , After the alarm occurs , Delete... In working memory Fire object , And then test Alarm Whether the object still exists .

2.1.2 drl Documentation

package rules

import com.huan.drools.insertmethod.Fire
import com.huan.drools.insertmethod.Alarm

rule "insert_ When there is a fire , Insert the alarm object into the working memory "
    when
        $fire: Fire()
    then
        System.out.println("1、 When there is a fire , Insert the alarm object into the working memory ");
        insert(new Alarm($fire));
end

rule "insert_ When there is an alarm object in the rule memory , Alarm , Then delete the fire object "
    when
        $fire: Fire()
        $alarm: Alarm( fire == $fire )
    then
        System.out.println("2、 Alarm , Then delete the corresponding fire object ");
end

rule "insert_ Check whether the alarm object still exists -01"
    when
        Alarm()
    then
        System.out.println("3、insert  The inserted alarm object still exists ");
        //  Delete... In working memory Fire object 
        delete($fire);
end

rule "insert_ Detect that the alarm object does not exist "
    when
        not Alarm()
    then
        System.out.println("3、insert  The inserted alarm object does not exist ");
end

What is used here is insert Insert

2.1.3 part java Code writing

//  Insert the fire object into the working memory 
kieSession.insert(new Fire());
//  Only trigger the rule name with  insert_  Opening rule 
kieSession.fireAllRules(new RuleNameStartsWithAgendaFilter("insert_"));

2.1.4 Running results

1、 When there is a fire , Insert the alarm object into the working memory 
2、 Alarm , Then delete the corresponding fire object 
3、insert  The inserted alarm object still exists 

2.1.5 Conclusion

1. insert You can insert... Into working memory Fact object .
2. insert After method call , This will result in pattern re matching , Lead to rules that will not be executed before , Re execution .
3. insert Method to insert an object into working memory , When the rules don't hold , Will not automatically delete , Manual deletion required , Pay attention to and insertLogical The difference between

2.2 insertLogical Insert object into working memory

insert Is to insert objects into working memory , At the same time, it will lead to the re pattern matching of rules . At the same time, when the rules are not satisfied , It will be deleted automatically .

2.2.1 demand

When there is a fire Fire when , Insert a... Into the working memory Alarm object , After the alarm occurs , Delete... In working memory Fire object , And then test Alarm Whether the object still exists .

2.2.2 drl Documentation

package rules

import com.huan.drools.Fire
import com.huan.drools.Alarm

rule "insertLogical_ When there is a fire , Insert the alarm object into the working memory "
    when
        $fire: Fire()
    then
        System.out.println("1、 When there is a fire , Insert the alarm object into the working memory ");
        insertLogical(new Alarm($fire));
end

rule "insertLogical_ When there is an alarm object in the rule memory , Alarm , Then delete the fire object "
    when
        $fire: Fire()
        $alarm: Alarm( fire == $fire )
    then
        System.out.println("2、 Alarm , Then delete the corresponding fire object ");
        delete($fire);
end

rule "insertLogical_ Check whether the alarm object still exists -01"
    when
        Alarm()
    then
        System.out.println("3、insertLogical  The inserted alarm object still exists ");
end

rule "insertLogical_ Detect that the alarm object does not exist "
    when
        not Alarm()
    then
        System.out.println("3、insertLogical  The inserted alarm object does not exist ");
end

What is used here is insertLogical Insert

2.2.3 part java Code writing

kieSession.insert(new Fire());
kieSession.fireAllRules(new RuleNameStartsWithAgendaFilter("insertLogical_"));

2.2.4 Running results

1、 When there is a fire , Insert the alarm object into the working memory 
2、 Alarm , Then delete the corresponding fire object 
3、insertLogical  The inserted alarm object does not exist 

2.2.5 Conclusion

1. insertLogical You can insert... Into working memory Fact object .
2. insertLogical After method call , This will result in pattern re matching , Lead to rules that will not be executed before , Re execution .
3. insertLogical Method to insert an object into working memory , When the rules don't hold , Will automatically delete attention and insert The difference between

2.3、update Update objects in working memory

update: Use it to specify the fields to be updated and the entire related fields Fact, And notify... Of the change Drools engine . Fact After the change , You must call before changing another fact that may be affected by the updated value update. To avoid this, add steps , Please switch to modify Method .

2.3.1 demand

Rule one ： When there is a fire object in the working memory Fire, And the name name Trigger rule when null , At the same time, set the name of the fire as a great fire .
Rule 2 ： When a fire exists , Output fire name

2.3.2 drl Documentation

package rules

import com.huan.drools.Fire
import com.huan.drools.Alarm

rule "update_ When there is a fire object , Set a name for the fire "
    when
        $fire: Fire(name == null)
    then
        System.out.println("1、 Set fire name ");
        $fire.setName(" a great fire ");
        update($fire)
end

rule "update_ Trigger when the name of the fire object exists "
    when
        $fire: Fire(name != null)
    then
        System.out.println("2、 The name of the fire object is : " + $fire.getName());
end

2.3.3 part java Documentation

kieSession.insert(new Fire());
kieSession.fireAllRules(new RuleNameStartsWithAgendaFilter("update_"));

2.3.4 Running results

1、 Set fire name 
2、 The name of the fire object is :  a great fire 

2.3.4 Conclusion

1. update This will result in pattern re matching .
2. update Will modify the value in the working object memory .

2.4、modify Update objects in working memory

modify： Use it to specify to be Fact Object and notify you of the changes Drools engine . This method provides a structured fact update method . It will update the operation with setter Call to change object fields .

2.4.1 demand

Rule one ： When there is a fire object in the working memory Fire, And the name name Trigger rule when null , At the same time, set the name of the fire as a great fire .
Rule 2 ： When a fire exists , Output fire name

2.4.2 drl Documentation

package rules

import com.huan.drools.Fire
import com.huan.drools.Alarm

rule "modify_ When there is a fire object , Set a name for the fire "
    when
        $fire: Fire(name == null)
    then
        System.out.println("1、 Set fire name ");
        modify($fire){
    
            setName(" a great fire ")
        }
end

rule "modify_ Trigger when the name of the fire object exists "
    when
        $fire: Fire(name != null)
    then
        System.out.println("2、 The name of the fire object is : " + $fire.getName());
end

2.4.3 part java Documentation

kieSession.insert(new Fire());
kieSession.fireAllRules(new RuleNameStartsWithAgendaFilter("modify_"));

2.4.4 Running results

1、 Set fire name 
2、 The name of the fire object is :  a great fire 

2.4.5 Conclusion

1. modify This will result in pattern re matching .
2. modify Will modify the value in the working object memory .
3. In general use modify, Do not use update.

2.5 delete Delete objects in working memory

usage ：delete(<object>)

retract Also and delete Same effect , But it is recommended delete.

3、drools Simple use of variables

package rules

rule "drools_ Use of variables "
    when
        eval(true)
    then
        System.out.println("Match Active current trigger rule : " + drools.getMatch());
        System.out.println(" The name of the current trigger rule : " + drools.getRule().getName());
        // System.out.println(" Terminate rule execution fireUntilHalt(): " + drools.getKieRuntime().halt());
        // System.out.println(" Activate AgendaGroup Group : " + drools.getKieRuntime().getAgenda().getAgendaGroup( "CleanUp" ).setFocus());

        System.out.println(" Get all global variables : " + drools.getKieRuntime().getGlobals());
        // System.out.println(" Set global variables ：" + drools.getKieRuntime().setGlobal("username","huan"); );
        // System.out.println(" Get query results ：" + drools.getKieRuntime().getQueryResults());
end

4、 Inheritance of rules

4.1 demand

Rule one ： If the user (customer) In the age of (age) Greater than 60 year , Then beat 0.9 fold .
Rule 2 ： On the basis of rule one , If the user has a car (car), You can park for free (freeParking).

4.2 drl Documentation

package rules

import com.huan.drools.Customer
import com.huan.drools.Car

rule "rule_extends_ Rule one "
    when
        $c: Customer(age > 60)
    then
        modify($c){
    
            setDiscount(0.9)
        }
        System.out.println(" Trigger rule 1 ： User age >60 year , hit 0.9 fold ");
end

//  Rule two inherits the condition of rule one 
rule "rule_extends_ Rule 2 " extends "rule_extends_ Rule one "
    when
        $car: Car()
    then
        modify($car){
    
            setFreeParking(true)
        }
        System.out.println(" Trigger rule 2 ： The user has a car , Free parking ");
end

here rule_extends_ Rule 2 Inherited rule_extends_ Rule one , So the conditions of rule 1 also inherit .

4.3 part java Code

Car car = new Car();
Customer customer = new Customer();
customer.setAge(65);
kieSession.insert(customer);
kieSession.insert(car);
kieSession.fireAllRules(new RuleNameStartsWithAgendaFilter("rule_extends_"));

The customer has a car , And the age is 65 year , Satisfy rules 1 and 2 above

4.4 Running results

 Trigger rule 1 ： User age >60 year , hit 0.9 fold 
 Trigger rule 2 ： The user has a car , Free parking 

4.5 Conclusion

You can see in the rule Upper use extends keyword , You can implement rule inheritance .

5、 Use do[…] Syntax rewrite the example inherited above

5.1 demand

As long as the user is greater than 60 year , Direct hit 0.9 fold , If there's a car , You can park for free .

5.2 drl Documentation

package rules

import com.huan.drools.Customer
import com.huan.drools.Car

rule " Name the result _rule"
    when
        $c: Customer(age > 60)
        do[giveDiscount] //  When the above condition holds, execute  then [giveDiscount]
        $car: Car() //  When this condition holds , Execute the default  then
    then
        modify($car){
    
            setFreeParking(true)
        };
        System.out.println(" The user has a car , Free parking ");
    then [giveDiscount]
        modify($c){
    
            setDiscount(0.9)
        };
        System.out.println(" User age >60 year , hit 0.9 fold ");
end

explain ： See the rule file above

5.3 part java Code writing

Car car = new Car();
Customer customer = new Customer();
customer.setAge(65);
kieSession.insert(customer);
kieSession.insert(car);
kieSession.fireAllRules(new RuleNameStartsWithAgendaFilter(" Name the result _"));

5.4 Running results

 User age >60 year , hit 0.9 fold 
 The user has a car , Free parking 

It also realizes the requirements

5.5 Conclusion

adopt when Use in do[ name ] then thenthen name It can also be realized .

6、 Realization if else if The effect of

6.1 demand

Finish something like if else if else effect . See various execution results below .

6.2 Rules file

rule "if else-if"
    when
       $customer: Customer(age > 60) //  Rule memory exists Customer object , also age>60
        if($customer.getLevel() == 1) do[level1] //  User level is 1, perform then[level1], Then continue to execute the following conditions 
        else if ($customer.getLevel() == 2) break[level2] //  User level is 2, perform then[level2], Do not execute the following conditions 
        else do[levelOther] //  Other level Level , perform then[levelOther], Then execute the following conditions 
        Car()
    then
        System.out.println(" I did ");
    then[level1]
        System.out.println("level1");
    then[level2]
        System.out.println("level2");
    then[levelOther]
        System.out.println("levelOther");
end

6.3 Execution result diagram

6.4 Various execution results - That's the explanation above

1、Customer Of age Less than 60.
Output ： No output .
2、Customer Of age Greater than 60 also level=1, No, Car.
Output ： level1
3、Customer Of age Greater than 60 also level=1, Yes Car.
Output ： level1 I did
4、Customer Of age Greater than 60 also level=2, No, Car.
Output ： level2
5、Customer Of age Greater than 60 also level=2, Yes Car.
Output ： level2
6、Customer Of age Greater than 60 also level=3, No, Car.
Output ： levelOther
7、Customer Of age Greater than 60 also level=3, Yes Car.
Output ： levelOther I did

6.5 do and break What's the difference?

do： After execution , We will continue to judge the following execution conditions . （ That is, the following Car Judge , According to whether there is Car Get different results ）
break： After execution , Will not judge the execution conditions behind .（ That is, the following Car Judge ,rule performed ）

7、 Complete code

https://gitee.com/huan1993/spring-cloud-parent/tree/master/drools/drools-drl-then

8、 Reference documents

1、https://docs.drools.org/7.69.0.Final/drools-docs/html_single/index.html#drl-rules-THEN-con_drl-rules