OK. Another one. How do I access and use a property of a member variable ( object ) of an object, in rules ?

e.g. in the same example, I need to check

1) if a product of type ‘laptop’ is inserted in memory AND

2) if the product’s MEMORY property ( object ) has an object of type DDR ram attached.

In other words, here is the relationship of facts -

PRODUCT has member variable MEMORY ( which is an object )

MEMORY has member variable RAM ( which is again an object )

RAM has member variable TYPE ( which should be equal to “DDR” )

From within rules ‘when’ part, how do I check if there is a PRODUCT inserted in memory whose MEMORY has a RAM of type DDR assigned ?

Regards,

Abhay Chaware

P Please consider the environment before printing this e-mail

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Michael Anstis
Sent: Monday, May 09, 2011 4:27 PM
To: Rules Users List
Subject: Re: [rules-users] FW: Basic rules question

Yes :)

2011/5/9 Abhay B. Chaware <Abhay.Chaware@kpitcummins.com>

Mike,

What I meant was, There are say 10 objects of RAM in memory whose type is DDR. Now my “Product” object has a member variable named “compatibleRAMs”, and I would like to set an arraylist containing these 10 objects to the “compatibleRAMs” variable of “Product” object in memory.

I am reading about the “collect” which can be used to create collections from fact objects in memory. Something like.

When

$prod : Product (type==’laptop’)

$compatibleRAMs : ArrayList() from collect (RAM (type == ‘DDR’))

Then

$prod.setCompatibleRAMs($compatibleRAMs);

Am I on the right track ?

-abhay

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Michael Anstis
Sent: Monday, May 09, 2011 3:52 PM
To: Rules Users List
Subject: Re: [rules-users] FW: Basic rules question

Abhay,

Do you need a list?

You can assign RAM to COMPUTERS with this:-

when
    $c : Computer( $type : type )
    $r : RAM( compatibleWith == $type )
then
   $c.addRAM( $r );
end

This would add all RAM (in Working Memory) compatible with COMPUTER to computer.

You could use a list of RAM as a Fact in WM and change your rule to use that:-

when
    $l : MyList( )
    $c : Computer( $type : type )
    $r : RAM( compatibleWith == $type ) from $l
then
    $c.addRAM( $r );
end

Or you can define a rule to construct the list too:-

when
    $l : MyList( $t : typeRAM )
    RAM( $c : $t )
then
    $l.add( $r )
end

I assume you'd need to differentiate different lists for different types; so I have shown use of "MyList" which could subclass ArrayList and have a "Type of RAM" attribute. Drools doesn't "do" generics.

With kind regards,

Mike

2011/5/9 Abhay B. Chaware <Abhay.Chaware@kpitcummins.com>

Wendy,

Thanks for helping me out so far.

I have another question. What if I have all my “RAM” objects inserted into working memory. How should I write my rule’s “when” portion to get a collection of all the RAM objects matching type “DDR” ? In other words, can I get collection of facts assigned to a variable and use it in the “then” part ?

Thanks

Abhay

==================================

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Wendy Mungovan
Sent: Friday, May 06, 2011 5:47 PM
To: Rules Users List
Subject: Re: [rules-users] Basic rules question

Q2:
So the rule would be something like:

rule "RAM type"
when
     $product: Product(type == "laptop");
then
     //you are looking for the best way to set valid RAM types in the then part of the rule?
    $product.setRamType("DDR");
    //or
   $product.setValidRamOptions( getValidRamOptions("DDR"));
end

where getValidRamOptions would be a custom function included through 'import function' so you can then load the choices from some where else. Or if RamOptions were an object in memory you could have a rule like:

rule "RAM type"
when
     $product: Product(type == "laptop");
     $ramOptions: RAMOptions(type == "DDR");

then
   $product.setValidRamOptions( $ramOptions.getList());
end

Wendy

==================================

Regards,

Abhay Chaware

P Please consider the environment before printing this e-mail

Abhay,
Q1: I think that this will depend on how many different products you have. If there is a small number it is more straight forward to have a rule for each one (so the 2nd option). This allows all you logic to be in one place. If there are a large number of products and writing a rule for each one is intractable you probably would want to look into some generalizations of the rules. Is that helpful?

Q2: I'm not quite sure what you are getting at in Q2. Are you trying to write validation rules or rules that are modifying the facts?

Wendy

From: Abhay B. Chaware <Abhay.Chaware@kpitcummins.com>
To: "rules-users@lists.jboss.org" <rules-users@lists.jboss.org>
Sent: Fri, May 6, 2011 4:59:46 AM
Subject: [rules-users] Basic rules question

I am a newbie to rule based applications and trying to get the concept of rules. I have couple of questions about rules to start with, not specifically about Drools though.

Q1 - Should rules be data/model specific or can/should they be generic or both

==========================================================

e.g.

If selected product “TYPE” is “laptop”, then category “RAM” should have all “DDR” type items compatible ( selecting items matching certain property )

If selected product is “IBM T42”, then category “RAM” should have “512MB DDR” , “1024MB DDR”, “2048MB DDR” compatible. ( assigning individual items in rules )

Combination of both

Q2 – How should be the data modeled in above case

==========================================================

e.g.

in product master, each item ( e.g. T40, T42 ) should have a “TYPE” ( e.g. desktop or laptop ) , all items in category “RAM” should have a “TYPE” ( e.g. DDR ) and then control the assignment of RAM options to the PRODUCT through Rule using “DDR” type ?

in product master, each item ( e.g. T40, T42 ) should have a “TYPE” ( e.g. desktop or laptop ) , all items in category “RAM” should have a “compatibleProduct” column ( e.g. desktop or laptop ) and control the assignment of RAM to PRODUCT through “dynamic” rules by selecting all the RAMs by passing the “TYPE” of the product to the database handler.

Am I making my point clear ?

Thanks

Abhay

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