Jahia Modules - Rules

Each module in JAHIA can define its own rules, extend the rule domain specific language and add its own set of global objects.

How to add rules in a module?

Just define a rules.drl file at the root level of the module. An example from the tasks module:

###############################################################################
package org.jahia.modules.tasks.rules

#list any import classes here.
import org.jahia.services.content.rules.*
import org.slf4j.Logger

expander rules.dsl

#declare any global variables here
global User user
global Service service
global Logger logger
global Tasks tasks
###############################################################################

rule "A welcome task for the new user"
   when
       A new node is created
                - the node has the type jnt:user
   then
       Log "Creating welcome task for new user: " + node.getName()
       Create task "Welcome to Jahia!" with description "We are glad to have you in our platform." for user node.getName()
end

rule "A notification about new group member"
   when
       A new node is created
                - the node has the type jnt:member
       The node has a parent
   then
       Log "Notifying members of the group '" + parent.getParent().getName() + "' about new member '" + node.getName()
       Create task "New member in the group" with description "A new member was added to the group." for members of group parent.getParent().getName()
end

rule "A task has been created"
    when
        A new node is created
        - the node has the type jnt:task
        The node has a property assignee
    then
        Set the property state of the node with the value "active"
        Assign permissions "rw-" on the node to the user property.getNode().getName()
end

This file defines some new rule conditions that are not part of the default definition file:

  Create task "Welcome to Jahia!" with description "We are glad to have you in our platform." for user node.getName()

And it also defines a global object of type Tasks named tasks:

  global Tasks tasks

How do I extend the domain specific language for my rules ?

It is also very simple. You only have to add a rules.dsl file at the root level of your module. An example from the tasks module:

[consequence][]Create task "{title}" with description "{description}" for user {forUser}=tasks.createTask({forUser}, "{title}", "{description}", drools);
[consequence][]Create task "{title}" with description "{description}" for members of group {group}=tasks.createTaskForGroupMembers({group}, "{title}", "{description}", drools);

The extension made in a module will be available for all other modules, so if your modules rely on dsl from another module think of adding this module as a dependency of yours in the manifest file.

Here is an example of using tasks in your own module (say, Jahia RSS Feeds module):

  1. In templates/rss/META-INF/MANIFEST.MF we have:
      depends: Jahia Tasks
  2. And the templates/rss/rules.drl file content is:
    ###############################################################################
package org.jahia.modules.rss.rules

#list any import classes here.
import org.slf4j.Logger
import org.jahia.services.content.rules.*
import org.jahia.modules.tasks.rules.*

expander rules.dsl

#declare any global variables here
global User user
global Service service
global Logger logger
global Tasks tasks
###############################################################################

rule "Notification about new RSS feed"
   when
       A new node is created
                - the node has the type jnt:rss
        The node has a property url
   then
       Log "Notifying root about new RSS feed " + property.getStringValue()
       Create task "New RSS feed alert" with description "Read the newly added RSS feed, retrieved from '" + property.getStringValue() + "'" for user "root"
end

Note that the rule file must import the org.jahia.modules.tasks.rules.* package and have a definition for tasks global object, i.e.:

...
import org.jahia.modules.tasks.rules.*

...
global Tasks tasks
...

How do I add my own global objects to my rule context for execution?

Define a spring file in your module (META-INF/spring/module-name.xml). Define a bean of type ModuleGlobalObject. Example from the tasks module:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean class="org.jahia.services.content.rules.ModuleGlobalObject">
        <property name="globalRulesObject">
            <map>
                <entry key="tasks">
                    <bean class="org.jahia.modules.tasks.rules.Tasks" factory-method="getInstance">
                        <property name="taskService" ref="org.jahia.services.tasks.TaskService"/>
                    </bean>
                </entry>
            </map>
        </property>
    </bean>
</beans>

As for the dsl all modules will share the same set of global objects so be sure that the key, you use, is unique across all modules.