Loading and updating rules from a database in Drools 6

java drools
user506069 picture user506069 · May 14, 2015 · Viewed 11.3k times · Source

How would one go about loading rules from a database table at startup and updating them from the same table in Drools 6.2.0? I've found an example using Drools 5 that I could probably convert from Scala to Java but it looks like the API has changed pretty drastically... I don't see the RuleBaseFactory class, for example.

Any sample or documentation would be appreciated.

Answer

laune picture laune · May 14, 2015

I'm not sure from where that org.drools.RuleBaseFactory was taken. Below is how it was done in Drools 5.3 (and possibly earlier) up to 5.6:

KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
kbuilder.add( ..., ResourceType.DRL);
if( kbuilder.hasErrors() ){
    System.err.println( "### compilation errors ###" );
    KnowledgeBuilderErrors errors = kbuilder.getErrors();
    for( KnowledgeBuilderError err: errors ){
        System.err.println( err.toString() );
    }
    throw new IllegalStateException( "compile errors" );
}
KnowledgeBase kbase = kbuilder.newKnowledgeBase();
StatelessKnowledgeSession ksession = kbase.newStatelessKnowledgeSession();

The ellipsis indicates the place for inserting the data holding the rule text. Check the API for suitable types; a java.lang.String should be acceptable.

This is the way I use for 6.2:

KieServices kieServices = KieServices.Factory.get();
KieFileSystem kfs = kieServices.newKieFileSystem();
kfs.write( "src/main/resources/simple.drl", ... );
KieBuilder kieBuilder = kieServices.newKieBuilder( kfs ).buildAll();
Results results = kieBuilder.getResults();
if( results.hasMessages( Message.Level.ERROR ) ){
    System.out.println( results.getMessages() );
    throw new IllegalStateException( "### errors ###" );
}
KieContainer kieContainer =
    kieServices.newKieContainer( kieServices.getRepository().getDefaultReleaseId() );
KieBase kieBase = kieContainer.getKieBase();
kieSession = kieContainer.newKieSession();

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