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

[Wolfgang Laun]

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