[rules-users] Where is my understanding of Drools global variables wrong?

[milen igrachev]

Hello I tried what you proposed, it didn't do the trick. Then i reread the documentation and discovered:
"Globals are not designed to share data between rules and they should never be used for that purpose. 
Rules always reason and react to the working memory state, so if you want to pass data from rule to rule, 
assert the data as facts into the working memory." 
  Sadly, I was trying to do just that...

I am sorry for the question in first place.
I want to ask something (just to be sure).

If I want to share data between rules (in my case transitional calculation results, that are missing in my model),  the only way to do so is to pass them into some temporary facts?

Thanks again  
  Best Regards,
Milen






 -------- Оригинално писмо --------

От: Wolfgang Laun wolfgang.laun at gmail.com

Относно: Re: [rules-users] Where is my understanding of Drools global
 variables wrong?

До: Rules Users List  

Изпратено на: Понеделник, 2014, Февруари 3 18:09:26 EET


The typical misunderstanding is that a global is a "variable" in the

usual sense of the word. It is not.



When you set a global, you store an object in a map, using the

global's name as a key. Using a global in DRL code perfidiously and

conveniently hides the way the global is made available to the code in

a rule when you use the global's name just like any other variable:

You write the global's name, but you use a local copy.



If you intend to change the global existence of a global you'll have

to use the API that's used to set up a global in the first place: get

the session object, call setGlobal...



Cheers

Wolfgang









On 03/02/2014, milen igrachev  igrachev at abv.bg > wrote:

> Hello, for the first time I have the need to define a global variables in a

> DRL file, and from what it seems from the documentation it shall be a

> variable visible to all my rules in the

> DRL file. However I don't see what I do wrong, but the modifications made by

> one rule are not visible to the others.  Here is illustration of what I

> have:

>

> [Fact model code]

>  public class TestPOJO {   	 private int fieldOne;   	 private String

> fieldTwo;   	    	 public int getFieldOne() {...}   	 public void

> setFieldOne(int fieldOne) {...}   	 public String getFieldTwo() {...}   	

> public void setFieldTwo(String fieldTwo) {...}  }

>   [DRL rule code]

>  global java.lang.Double myGlobal;  rule "Your First Rule"   	 salience 2

>

>  when

>

>

>

>  TestPOJO(fieldOne > 10)

>

>  then

>

>

>

>  System.out.println("This is rule #1");

>

>

>

>  System.out.println(myGlobal);

>

>

>

>  myGlobal = 0.03;  end  rule "Your Second Rule"   	 salience 1

>

>  when

>

>

>

>  TestPOJO(fieldTwo == "true")

>

>  then

>

>

>

>  System.out.println("This is rule #2");

>

>

>

>  System.out.println(myGlobal);  end

>   [Call to Drools]

>  TestPOJO myTestFact = new TestPOJO();  myTestFact.setFieldOne(15);

> myTestFact.setFieldTwo("true");

>    KieServices ks = KieServices.Factory.get();  KieContainer kContainer =

> ks.getKieClasspathContainer();  KieSession kSession =

> kContainer.newKieSession("ksession-rules");

>

>   	   kSession.insert(myTestFact);  kSession.fireAllRules();

> kSession.dispose();

>   [Output]

>  This is rule #1  null  This is rule #2  null

>

>

> [What I expect to have as output]    This is rule #1  null  This is rule #2

> 0.03

>   I used the salience to set rule order to be sure that rule one is executed

> before rule two, but my global value is never updated.

> Can you please tell me where I do wrong? Can my expectations be met somehow,

> I need such type of internal rule variables to calculate temporary

> values and pass them between rules?

>

>   Thank you!!!

>

> Best Regards,  Milen

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