Dynamically load rules in drools rule engine running on top of Apache spark

[kemai...@gmail.com]

Hello,

We are planning to store the rules in some sort of datastore. Whenever a rule changes or a new one gets added, we would want to reload the rule engine(spark+drools) with the changes. Looking for some suggestions to achieve the same if someone is already doing it. Any help is really appreciated.

Thanks,

Kiran

[Ged Byrne]

This is easy to achieve using a virtual file system.  This is already built into the KieServices as the KieFileSystem.

The Javadoc is here:https://docs.jboss.org/jbpm/v6.0.Beta2/javadocs/org/kie/api/builder/KieFileSystem.html 

And here is the source of a Drools unit test making use of the KieFileSystem to load a rule from a string.

http://massapi.com/source/jboss/20/38/2038493886/org/drools/drools-persistence-jpa/6.0.0.Beta1/drools-persistence-jpa-6.0.0.Beta1-test-sources.jar/drools-persistence-jpa-6.0.0.Beta1-test-sources.jar.unzip/org/drools/persistence/kie/persistence/session/JpaPersistentStatefulSessionTest.java.html#90

The relevant bit looks like this:

        KieServices ks = KieServices.Factory.get();

        KieFileSystem kfs = ks.newKieFileSystem().write( "src/main/resources/r1.drl", str );

        ks.newKieBuilder( kfs ).buildAll();

All you have to do is pull the text of the rule definition from your DataStore (Spark or whatever) and add it to a path in your virtual filestore.

Make sure you follow the Maven conventions in your choice of path - it needs to go in a resource folder: http://maven.apache.org/plugins/maven-resources-plugin/examples/resource-directory.html

I don't think you can dynamically alter rules once a session has been built.  When your rules definitions change then you'll need to build a new session.  You can keep the same KieFileSystem and overwrite the file, but you'll need to build a new session.

If your sessions are statefull then take care to dispose of the previous session properly: https://docs.jboss.org/jbpm/v5.1/javadocs/org/drools/runtime/StatefulKnowledgeSession.html#dispose()