[rules-users] Mapping complex objects info Guvnor compatible shim classes?

[Stephen Masters]

Your plan seems about right to me. When working in pure Drools, you don't always need to do this. However, when working in Guvnor, I have always found it necessary to create a simplified domain model for facts.

In Guvnor, you can bind variables to fields and drill in, but it's fiddly. Guided rules are much more readable when they are dealing with matching bean-style facts with key attributes available through simple getX() accessor methods. And of course you definitely need the bean-style getX() methods.

The other thing to think about, is that when working with Guvnor, you should be avoiding any dependencies on external classes from within your facts. Otherwise, you will need to put everything on your Guvnor web server's class path, which totally messes with your ability to upload fact model updates. Yet another reason to keep them simple.


So given that you're going with that plan, here are my tips for the lazy (like me)...

To help with simplifying your transformations, it may be worth looking at Dozer or similar: http://dozer.sourceforge.net/

Personally, because I have often found that I'm doing things like mapping multiple objects into a single fact, I tend to just do the mapping in straight Java code. It tends not to be too painful, as I rarely find the need for bi-directional mappings. I don't often need to get a fact back out of working memory. So although it feels a bit naughty, I often avoid the fact-to-domain-object transform. :)

Think about what properties you really might want to write rules about. It's easy to spend a huge amount of time writing a huge fact model, and transforms for every single property of every class in your domain model. Truth is you probably won't write rules that look at all of it. So have a think about whether you do need to map everything or not. My tip here would be to follow a TDD approach. Look at what rules your users want to write. You should find that the rules mostly follow certain stereotypes, so create rule tests covering a representative selection of such stereotype (ensure coverage of all unique fact attributes which are examined). Create a fact model which can satisfy those tests. Create tests for transforming from your domain model to your fact model. Create transforms to that fact model. Assuming you have a reasonably iterative environment, you can add transforms for additional attributes when users have tried out the application and come up with new rule stereotypes they would like to work with.


As an alternative (or to complement the above), take a look at DSLs. Each DSL phrase becomes available in your guided editor, so you can have simple rule phrases which the users can understand, but underneath, you can have code which is drilling into nested objects.

I do hope that's helpful… :)

Steve



On 10 Aug 2013, at 00:47, Mark Bennett <mark.bennett at lucidworks.com> wrote:

> We want our domain experts to be able to create Guided Rules in Guvnor (5.5)
> 
> But Guvnor seems pretty limited about what it will accept, and how it will render it.
> 
> We're attempting to create adapter classes that will:
> * Allow us to expose a rich set of fields and methods in UI
> * Use as injected facts into the engine
> 
> Main issues we're having:
> * Native objects are nested, but Guvnor seems to want shallow
> * Our native objects can have different attributes (different schemas)
> - And you can't say getField( fieldName )
> * Some returned items can be multivalued, vs. singular
> 
> Our idea is:
> * Have admin send a prototypical request & schema event into our native system
> * Scrape and flatten that into a java class that exposes Guvnor friendly methods
> * Send that class into Guvnor
> * Keep a copy of that class to create instances of when injecting facts into the engine
> 
> Is there some type of easy way to map complex objects to/from the simpler Guvnor/Drools model?  Some type of reflection based mapper with some simple rules or a template?  We're wondering what others have done in this situation?
> 
> Thanks,
> Mark
> 
> --
> Mark Bennett / LucidWorks: Search & Big Data / mark.bennett at lucidworks.com
> Office: 408-898-4201 / Telecommute: 408-733-0387 / Cell: 408-829-6513
> 
> 
> _______________________________________________
> rules-users mailing list
> rules-users at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.jboss.org/pipermail/rules-users/attachments/20130810/e3bb2678/attachment.html