[rules-users] Does Drools Fusion support "Group By" clause ?

[Edson Tirelli]

   Kiran,

   We don't have "syntax sugar" for group by yet, and so for cases
where your grouping expression is an attribute of a summarized object
and not an entity by itself, you need to use a trick. It can be
written in a single rule, but I recommend using a "registration" rule:

declare SaleType
    type : String
end

rule "register types"
when
     Sale( $type : type )
then
     insertLogical( new SaleType( $type ) );
end

   And then you can group by SaleType on your accumulation rules.

   It is on our todo list to provide better support for this case.

   Edson


2011/1/3 Kiran Ananthpur Bacche (kbacche) <kbacche at cisco.com>:
> Hi Gabor,
>
> Thanks for your response.
>
> I looked at this example in the user guide. In this example, there are
> two Event POJO (Order.java and OrderItem.java) that are injected.
> The example I quoted initially is slightly different. There is only one
> Event Pojo (Sale.java). The "type" can be a string or int attribute in
> Sale.java that can hold any random value. So it is not possible to make
> it a new Event POJO (Type.java), and insert all possible instances with
> different possible values.
>
> This requirement is for a CEP Engine. I used ESPER, and could achieve
> this easily using the "group by" clause in the EPL language.
>
> Withn DROOLs FUSION, Im not able to do the same.
>
> Thanks
>  Kiran
>
> -----Original Message-----
> From: rules-users-bounces at lists.jboss.org
> [mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Gabor Szokoli
> Sent: Monday, January 03, 2011 5:31 PM
> To: Rules Users List
> Subject: Re: [rules-users] Does Drools Fusion support "Group By" clause
> ?
>
> Hi,
>
> 2011/1/3 Kiran Ananthpur Bacche (kbacche) <kbacche at cisco.com>:
>> I want the rule to fire successfully only when the TotalSalesAmount
> for
>> _any_ given type exceeds 100.
>
> I've never used "accumulate" myself, so I looked it up in the manual,
> and there's an example that's exactly what you want :-)
> (just substitute $order with your $type)
>
> rule "Apply 10% discount to orders over US$ 100,00"
> when
>    $order : Order()
>    $total : Number( doubleValue > 100 )
>             from accumulate( OrderItem( order == $order, $value : value
> ),
>                              sum( $value ) )
> then
>    # apply discount to $order
> end
>
> http://downloads.jboss.com/drools/docs/5.1.1.34858.FINAL/drools-expert/h
> tml_single/index.html#d0e4893
>
>
>
> Gabor
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-- 
  Edson Tirelli
  JBoss Drools Core Development
  JBoss by Red Hat @ www.jboss.com