[rules-users] using null in drools rulebase

[Edson Tirelli]

    Mike,

    The implicit connective constraint is AND, so if you write:

when
Beak(beak == "small beak", beak = null)


    You are saying:

When beak is "small beak" AND beak is null...

    Which will always evaluate to false.

     []s
     Edson

mike20043 wrote:

>hi everyone
>
>need a bit more help here. im currently attempting to write some rules into
>my rulesbase and can't seem to get the system to check if a variable is
>empty. i have tried using null as shown in the code below
>
>
>rule "small beak + small body + garden"
>	when
>	Beak(beak == "small beak", beak = null) &&
>	Body(body == "small body")
>	Location(location == "garden")
>	then 
>		ES.resultsmx("<p> );
>		ES.resultsmx( Robin </p>");
>		ES.resultsop();
>end
>
>
>
>which dosent work but for some reason i am able to check if it is not null
>by doing this
>
>
>rule "small beak + small body + garden"
>	when
>	Beak(beak == "small beak", beak != null) &&
>	Body(body == "small body")
>	Location(location == "garden")
>	then 
>		ES.resultsmx("<p> );
>		ES.resultsmx( Robin </p>");
>		ES.resultsop();
>end
>
>
>
>I have tired using == null but this returns a false and the rule dosent run.
>can anyone help me please. Also if anyone has any knowledge of how to write
>rules so it only outputs one result instead of repeatedly running the
>conditions and outputting results for each correct condition and also how to
>check if a string variable contains a substring (within a rule) that would
>be greatly appreciated . Thanks in advance
>
>mike
>  
>


-- 
 Edson Tirelli
 Software Engineer - JBoss Rules Core Developer
 Office: +55 11 3124-6000
 Mobile: +55 11 9218-4151
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