[rules-users] Drools - Doing Complex Stuff inside a Rule Condition or Consequence

[Mauricio Salatino]

Hi Miguel,
Drools is flexible enough to let you choose based on the scenario that you
have. It really depends if you want to go and lookup the information at
runtime or if you can go first load all the facts that you want to use and
do the inference.
Imagine that if you want to go to the database in runtime you will have
performance consequences if the rule get's evaluated a lot of times. Just my
two cents.
Greetings.

2010/11/29 Miguel Fernando Cabrera <mfcabrera at gmail.com>

> Hello everyone
>
> In my company we are planning to use Drools for couple of projects and we
> having some questions about the best way to use it
>
> My question is what should be and shouldn't be done inside a Rule
> Condition/Consequence. Given that we can write Java directly or call methods
> (for example From a Global object in the Working Memory).
>
> Example. Given a Rule that evaluates a generic Object (e.g. Person) have
> property set to true. Now, that specific propertie can only be defined for
> that Object going to the database (or going to a web service) and fetching
> that info. So we have two ways of implementing that:
>
> *Alternative A:*
>
>    - Go to the database and fetch the object property (true/false, a code)
>    - Insert the Object in the working memory
>    - Evaluate the rule
>
> *Alternative B:*
>
>
>    - Insert a Global Object that has a method that connects to the
>    database and check for the property for the given object.
>    - Insert the Object to eval in Working Memory
>    - In the rule, call the Global Object and perform the access to the
>    database
>
>
> Which of those is considered better? I really like A,  but sometimes B is
> more straightforward, however what would happen if something like a
> Exception from the Database is raised?* *I have seen the alternative B
> implemented  in the Drools 5.0 Book from Packt Publishing,however they are
> doing a mocking and they don't talk about the actual implications of going
> to the database at all.
>
> Thank you in advance,
>
> --
> Miguel Fernando Cabrera Granados
> http://mfcabrera.com
> "A los hombres fuertes les pasa lo que a los barriletes; se elevan cuando
> es
> mayor el viento que se opone a su ascenso." - José Ingenieros
>
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>


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