[rules-users] Using rules with database scenario

[Marcus Ilgner]

On 3/9/07, Uday Kamath <UKamath at dharbor.com> wrote:
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> We had similar use case. What we do is we model the Schema elements,
> generate Java Beans (pojo), and write rules using these Pojo. Now we have
> written a Service on top which takes Hibernate QL and gets the database
> records as the same Pojos that Rules are defined on and fire the Rules. Thus
> the service is generic and can be changed to take any Query. The Rules can
> me modified and changed anytime and redeployed but business objects in form
> of Pojos remain the same. Hope this helps
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> -Uday
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>  ________________________________
>
>
> From: rules-users-bounces at lists.jboss.org
> [mailto:rules-users-bounces at lists.jboss.org] On Behalf Of
> Joe Chuby
>  Sent: Friday, March 09, 2007 3:53 AM
>  To: rules-users at lists.jboss.org
>  Subject: [rules-users] Using rules with database scenario
>
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> Hi all,
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>  First time trying to learn JBoss Rules here. We have a pretty large
> database (DBMS), we want to build some rules and retrieve data based on the
> rules.
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>  Could someone give a hint or an example of this usage scenario? I mean, how
> can I use rules for database query, without writing my rules in SQL
> directly? We are currently writing everything in HQL (Hibernate), but the
> rules change every 3 months on average, so that's not a way to maintain the
> system. Therefore, we want to extract that portion of the business logic out
> of the code. The data structure does not change, but the rules keep on
> changing.
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>  I'm reading the user's guide, running thru the examples, writing some of my
> own, but still no clue how to make it work with database.
>
>  If someone could give a sample, that would be greatly appreciated.
>
>  Thanks a lot.
>

That's probably the best solution. Using the current version (3.1M1),
you can use the FROM keyword to reference facts from List object
returned from a method call on a service, for example.
Something like this works very good in my current testing project:

rule foobar
when
  MyObject( someValue = "foobar" ) from MyObjectDAO.loadAll()
then
...
end

The DAO then uses Hibernate to load some objects and returns a
List<MyObject> which can be used by Drools.
As Uday already wrote, you could also write a DAO which retrieves
arbitrary objects using a given HQL statement.

Best regards
Marcus