14.3. Using rules from a jBPM process definition

A rule base can act as a jBPM action, decision, or assignment handler in either a pageflow or a business process definition.

<decision name="approval">         
  <handler class="org.jboss.seam.drools.DroolsDecisionHandler">
    <workingMemoryName>orderApprovalRulesWorkingMemory</workingMemoryName>
    <assertObjects>
      <element>#{customer}</element>
      <element>#{order}</element>
      <element>#{order.lineItems}</element>
    </assertObjects>
  </handler>
    
  <transition name="approved" to="ship">
    <action class="org.jboss.seam.drools.DroolsActionHandler">
      <workingMemoryName>shippingRulesWorkingMemory</workingMemoryName>
      <assertObjects>
        <element>#{customer}</element>
        <element>#{order}</element>
        <element>#{order.lineItems}</element>
      </assertObjects>
    </action>
  </transition>  
  <transition name="rejected" to="cancelled"/> 
</decision>

The <assertObjects> element specifies EL expressions that return an object or collection of objects to be asserted as facts into the WorkingMemory.

Using Drools for jBPM task assignments is also supported:

<task-node name="review">
  <task name="review" description="Review Order">
    <assignment handler="org.jboss.seam.drools.DroolsAssignmentHandler">
      <workingMemoryName>
        orderApprovalRulesWorkingMemory
      </workingMemoryName>
      <assertObjects>
        <element>#{actor}</element>
        <element>#{customer}</element>
        <element>#{order}</element>
        <element>#{order.lineItems}</element>
      </assertObjects>
    </assignment>
  </task>
  <transition name="rejected" to="cancelled"/>
  <transition name="approved" to="approved"/>
</task-node>

Certain objects are available as Drools globals — the jBPM Assignable is available as assignable, and the Seam Decision object is available as decision. Rules that handle decisions should call decision.setOutcome("result") to determine the decision result. Rules that perform assignments should set the actor ID with Assignable.

package org.jboss.seam.examples.shop
import org.jboss.seam.drools.Decision 
global Decision decision 
rule "Approve Order For Loyal Customer" 
  when 
    Customer( loyaltyStatus == "GOLD" ) 
    Order( totalAmount <= 10000 ) 
  then 
    decision.setOutcome("approved"); 
end

package org.jboss.seam.examples.shop 
import org.jbpm.taskmgmt.exe.Assignable 
global Assignable assignable 
rule "Assign Review For Small Order" 
  when 
    Order( totalAmount <= 100 ) 
  then 
    assignable.setPooledActors( new String[] {"reviewers"} ); 
end

Note

More information about Drools is available at http://www.drools.org.

Important

Seam comes packaged with enough Drools dependencies to implement some simple rules. To add extra capabilities, download the full Drools distribution and add extra dependencies as required.