[rules-users] Problem calling a function returning String

[Greg Barton]

In general the use of static method calls in conditions when the return values could change is not recommended.  Things can get wiggy, as you've already seen.

The rule conditions are evaluated when the objects they match on are inserted into working memory.  In your case, though, the rule doesn't match on any object, so the condition evaluates when the session is created. (That's my guess, at least.)  It's NOT when you call fireAllRules.  That only tells the session to fire rules that are currently eligible to fire.  So, if your sequence is this, nothing will happen:

<make session>
ValidationUtilities.evaVersionsNr = "1234";
fireAllRules()

However, this might work:

ValidationUtilities.evaVersionsNr = "1234";
<make session>
fireAllRules()

But, even if it does, it's not a good idea.  There's basically no way to inform the engine that ValidationUtilities.evaVersionsNr has changed, so your results could be unpredictable. (Especially as ValidationUtilities.evaVersionsNr is a public static member.  Oi!)

--- On Tue, 7/7/09, rainbowflower <al_aysha at yahoo.co.in> wrote:

> From: rainbowflower <al_aysha at yahoo.co.in>
> Subject: [rules-users] Problem calling a function returning String
> To: rules-users at lists.jboss.org
> Date: Tuesday, July 7, 2009, 10:33 AM
> 
> Hi all,
> 
> I am rather new to Drools and I have a problem using
> functions.
> 
> I have a rule like:
> 
> rule "rule 1"
>     when
>        
>    eval(getEVAVersionsNr() == "1234")
>         then
>        
>    System.out.println("rule fired");
> end
> 
> The getEVAVersionsNr() method is present in a Java class
> "ValidationUtilities.java", which I'm importing in my drl
> file and it looks
> like this:
> 
> public class ValidationUtilities {
>  
>   public static String evaVersionsNr; 
> 
> public static String getZEVAVersionsNummer()
> {   
>     return evaVersionsNr;   
>   }
> }
> 
> This static attribute "evaVersionsNr" is set to "1234" from
> another Java
> class before I fire my rules. So, I assume that the eval
> construct should
> return true. But, it does not return true and the
> consequence is not
> exected.
> 
> Further info:
> 
> When I modify my rule like:
> 
> rule "rule 1"
>     when
>            eval(true)
>         then
>        
>    System.out.println(getEVAVersionsNr());
> end
> 
> the consequence part is getting executed and 1234 is
> getting printed.
> 
> I am really lost and I could not find out what goes wrong.
> If someone could
> find out what I am missing, I shall be thankful.
> 
> Thanks in advance.
> -- 
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> 
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