[rules-users] using null in drools rulebase

[mike20043]

my bad, i copied the code from the wrong version. it should of been

Beak(beak == "small beak") || Beak(beak == null)

and it evaluates to false even if beak is null or dosent exist.

i have also tried using =null but i get a error message saying unexpected
token'beak'. 
strangely if i use !=null it does accept it and im just stumped.

mike.


Edson Tirelli-3 wrote:
> 
> 
>     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
>  JBoss, a division of Red Hat @ www.jboss.com
> 
> 
> _______________________________________________
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> 
> 

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