Drools facts using POJO accessor methods error

[aliosha79]

Hi,
i have some troubles to undestand how drools processes FACTS. I have a POJO class resulted from an UnMarshal jaxb processing like this:

public MyClass {

protected String className = "Class1";

public getClassName(){
        return className;
}

public setClassName(String className){
        this.className = className
}

}


Now i have to compose a drl file with a rule like this:


when
        $Class : MyClass()
        eval ($Class.getClassName() == "Class1")
then
        System.out.println("ok!!!");
end


This syntax doesn't rise errors BUT doesn't match the real name... no ok message are printed.


when
        $Class : MyClass (getClassName() == "Class1")
then
        System.out.println("ok!!!");
end

This syntax raises me a null pointer exception!!!


What's the right syntax?
Can i use the accessor methods building drools facts?
Thanks a lot!

[laune]

As soon as you use eval(), you are in Java-land where String
comparisons should not be made using "==".

There's nothing wrong with the second form, i.e., you can write (using
Drools 5.3.0)

   MyClass (getClassName() == "Class1")

although the simpler form is usually preferred:

  MyClass( className == "Class1" )

-W


On 27/02/2012, aliosha79 <[hidden email]> wrote:

> Hi,
> i have some troubles to undestand how drools processes FACTS. I have a POJO
> class resulted from an UnMarshal jaxb processing like this:
>
> public MyClass {
>
> protected String className = "Class1";
>
> public getClassName(){
>         return className;
> }
>
> public setClassName(String className){
>         this.className = className
> }
>
> }
>
>
> Now i have to compose a drl file with a rule like this:
>
>
> when
>         $Class : MyClass()
>         eval ($Class.getClassName() == "Class1")
> then
>         System.out.println("ok!!!");
> end
>
>
> This syntax doesn't rise errors BUT doesn't match the real name... no ok
> message are printed.
>
>
> when
>         $Class : MyClass (getClassName() == "Class1")
> then
>         System.out.println("ok!!!");
> end
>
> This syntax raises me a null pointer exception!!!
>
>
> What's the right syntax?
> Can i use the accessor methods building drools facts?
> Thanks a lot!
>
> --
> View this message in context:
> http://drools.46999.n3.nabble.com/Drools-facts-using-POJO-accessor-methods-error-tp3780387p3780387.html
> Sent from the Drools: User forum mailing list archive at Nabble.com.
> _______________________________________________
> rules-users mailing list
> [hidden email]
> https://lists.jboss.org/mailman/listinfo/rules-users
>

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[aliosha79]

ok thanks a lot!

[aliosha79]

what would be the right syntax using the second form, if i wanted to use two rows? like the first one?
Something like this?
when
        $Class : MyClass()
       
        $Class(className() == "Class1") ....... ?


thanks

[laune]

I'm not sure what you're asking, but I'm you'll find the answer easily enough by
reading the Expert documentation.
-W

On 27 February 2012 17:59, aliosha79 <[hidden email]> wrote:

what would be the right syntax using the second form, if i wanted to use two
rows? like the first one?
Something like this?
when
       $Class : MyClass()

       $Class(className() == "Class1") ....... ?


thanks

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[aliosha79]

Precisely i want to turn this form...

when
        $Class : MyClass (className() == "Class1")
then
        System.out.println("ok!!!");
end

into this:

when
        $Class : MyClass()
        ...($Class.className() == "Class1")
then
        System.out.println("ok!!!");
end

I need to declare the $Class variable separately... is it possible?
regards

[Davide Sottara]

Now this is an interesting use case.... could you please provide more details on why you're trying to do such a thing? Are you working on some kind of translator/analyzer?
Thanks
Davide

btw, taking constraints out of patterns does not seem the best way to use a RETE engine....
could you consider something like:

when
$Class : MyClass()
            MyClass( this == $Class, className == "Class1" )
then
  ...

or its equivalent, based on unification:

when
$Class := MyClass( )
$Class := MyClass( className == "Class1" )
then
 ....

[aliosha79]

my use case is:
XmlDocument ---> via JaxbUnmarshaller ---> POJO java Document

I m implementing a rule editor...
This ruleeditor analyzes the xmldocument and graphically allows me to build rules by selecting the document xml tree node... of course i can just build several rules in this way... but for the field which the project is located in, it's sufficient.
Now in those xml documents there could be sequences of elements which are turned into java list by Jaxb.
The problem is:
According to my xml nodes selection (ie the node is a list or not)... i have to be able to write the exact rule.
In the rule structure i have to find the constant parts and the variable ones.

For a normal node element a possible rule structure is:
when
$Class : MyClass( property == 123)
then
do somthing!
end

For a list instead:

when
$Class : MyClass ($list :listProperty)
...( this.ListItem.Quantity.Value ==123 ) from $list
then
do something!
end

So, i'm trying to find a common form with the minimum variable parts to be changed and to obtain a well written rule for both cases.

[Brad Davis]

Maybe you would be better off leveraging Guvnor for the Rules Editing.  Then you would just need to develop a hook that calls JAXB to take an XML Schema to a Pojo Object Model within the Guvnor system.

Brad Davis
Red Hat Consulting
Email: [hidden email] | c: 980.226.7865 | http://www.redhat.com 


----- Original Message -----
From: "aliosha79" <[hidden email]>
To: [hidden email]
Sent: Monday, February 27, 2012 1:30:41 PM
Subject: Re: [rules-users] Drools facts using POJO accessor methods error

my use case is:
XmlDocument ---> via JaxbUnmarshaller ---> POJO java Document

I m implementing a rule editor...
This ruleeditor analyzes the xmldocument and graphically allows me to build
rules by selecting the document xml tree node... of course i can just build
several rules in this way... but for the field which the project is located
in, it's sufficient.
Now in those xml documents there could be sequences of elements which are
turned into java list by Jaxb.
The problem is:
According to my xml nodes selection (ie the node is a list or not)... i have
to be able to write the exact rule.
In the rule structure i have to find the constant parts and the variable
ones.

For a normal node element a possible rule structure is:
when
$Class : MyClass( property == 123)
then
do somthing!
end

For a list instead:

when
$Class : MyClass ($list :listProperty)
...( this.ListItem.Quantity.Value ==123 ) from $list
then
do something!
end

So, i'm trying to find a common form with the minimum variable parts to be
changed and to obtain a well written rule for both cases.



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[aliosha79]

yes, thanks... but Guvnor has too much features for our aim