Drools terminates the execution of other rules after executing one rule

1、 background

In the process of our development , Maybe a scenario needs to write multiple rules , But some rules and other rules are mutually exclusive . That is, when a rule is established , Whether the rest of the rules are true or not , The rest of the rules are not enforced . So how to deal with this scenario ？

2、 demand

Suppose we have three rules rule-01、rule-02 and rule-03, When rule-02 After execution , that rule-03 Execution must be terminated .

3、 Implementation scheme

1、 adopt Fact Judge

When rule-02 After rule execution , modify Fact A property in , Setup rule executed , If subsequent rules are found to have been executed, they will not be executed .

2、 Judge by global variables

stay drools Use global variables to judge .

3、 adopt halt Method

When we're in drl Call in file drools.halt() After the method , It will immediately terminate the rules behind it , That is, the latter rules are not implemented .

Here we pass halt Method to implement .

4、 To achieve the above

4.1 drl Documentation

package rules

/**  demand ： stay  "rule-01"  and  "rule-02"  After the rule is executed , Termination Rules  "rule-03"  Implementation  */

rule "rule-01"
    salience 3
    when
    then
        System.out.println(drools.getRule().getName());
end

rule "rule-02"
    salience 2
    when
    then
        System.out.println(drools.getRule().getName());
        //  Terminate below  "rule-03"  Execution of rules 
        drools.halt();
end

rule "rule-03"
    salience 1
    when
    then
        System.out.println(drools.getRule().getName());
end

The above rules are relatively simple , adopt salience Set the priority of the rule , The higher the value, the higher the priority .when There are no conditions behind , Description rules will be through pattern matching , That is, it is possible to execute . however rule-02 Regular then Some have drools.halt(), explain , After the rule is executed , The rule activated after it needs to be terminated .

4.2 Running results

rule-01
rule-02

You can see rule-03 No output , This means that the rule has been terminated .

5、 Complete code

https://gitee.com/huan1993/spring-cloud-parent/tree/master/drools/drools-termination-rule