Drools is a Business Rules Management System (BRMS) solution. The plugin fully supports Drools kie-spring integration.
The plugin has been tested using the sample application and test script in the following environment:
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Drools 6.2.0.Final
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Grails versions 2.3.11 and 2.4.5
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OSX 10.10.3
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JDK 1.7.0_75
If you want to use the plugin with a version of Grails earlier than 2.3.0, see Grails 2.2.5 and Earlier.
If you have a question, problem, suggestion, or want to report a bug, please submit an issue. I will reply as soon as I can.
If you are upgrading from version 0.9.3, there are some breaking changes you will have to address.
Rule files and subdirectories must be located under src/resources/. You can no longer use some arbitrary file system path. This change and the one discussed below were required to align the plugin with Drools conventions.
grails.plugin.drools.drlFileLocation must be a single directory name and not a path. For example, the default of "rules" refers to the following file system path: src/resources/rules/.
Rule files are now available on the classpath using / instead of .. Older versions of the plugin violated the DRY principle by having the same rule file in two different locations. For example,
droolsService.executeFromFile("rules.ruleOne.drl", [facts])
becomes
droolsService.executeFromFile("rules/ruleOne.drl", [facts])
And
classLoader.getResourceAsStream("rules.ruleOne.drl")
becomes
classLoader.getResourceAsStream("rules/ruleOne.drl")
Rule files must have a "drl" or "rule" suffix. This change avoids unnecessary clutter in the target directory by omitting hidden files and directories.
The plugin offers a variety of ways to use rules. The RuleTests and TestController classes show several examples.
You can define beans using either a configuration file grails-app/conf/DroolsConfig.groovy or an xml file grails-app/conf/drools-context.xml. This will allow you to do something like this:
class SomeService {
def packageOneStatelessSession
def someMethod() {
def fact1 = SomeDomain.get(123)
def fact2 = SomeOtherDomain.get(123)
def facts = [fact1, fact2]
packageOneStatelessSession.execute(facts)
}
}
The DroolsService offers several methods to use rules stored in a database or on the file system (classpath). For example, assuming you have several rules in the database with a packageName of "ticket", you could do something like this:
class SomeOtherService {
def droolsService
def someMethod() {
def fact1 = SomeDomain.get(123)
def fact2 = SomeOtherDomain.get(123)
droolsService.fireFromDatabase("ticket", [fact1, fact2])
}
}
Edit your BuildConfig.groovy:
plugins {
// other plugins
compile ":drools:1.0.1"
}
Although Grails prefers convention over configuration, you cannot avoid some configuration for the Drools beans.
After the plugin is installed you will find a heavily commented DroolsConfig.groovy in grails-app/conf/ that you can use as a starting point for configuring your beans. When your application is compiled this file is parsed and grails-app/conf/drools-context.xml is created (or overwritten). For example, DroolsTestConfig.groovy is the one used for plugin integration tests.
There are two options that you can configure in your grails-app/conf/BuildConfig.groovy. The defaults are shown below:
grails.plugin.drools.configurationType = "droolsConfigGroovy"
grails.plugin.drools.drlFileLocation = "rules"
The option below will stop the plugin from overwriting grails-app/conf/drools-context.xml. This will allow you to edit the file manually without losing changes.
grails.plugin.drools.configurationType = "droolsContextXml"
This option is the directory root for Rule files, those files with a "drl" or "rule" suffix. Note the lack of leading and trailing slashes below:
grails.plugin.drools.drlFileLocation = "drools-rules"
You can take advantage of rule packages by creating subdirectories under drlFileLocation. See the plugin's src/resources/rules for an example.
All files in this directory and its subdirectories with a "drl" or "rule" suffix will be copied to the classpath.
If you change the domain class used to store your rules without using the script create-drools-domain, you will have to edit the corresponding configuration option in your grails-app/conf/Config.groovy.
grails.plugin.drools.droolsRuleDomainClass = "com.example.DroolsRule"
See DroolsConfig.groovy for configuration options and instructions. Drools Spring Integration provides more information.
Changes to rule files will not be available until the applicaiton is restarted.
Changing the grails.plugin.drools.drlFileLocation option could affect the packages property for a KieBase. For example, for the option
grails.plugin.drools.drlFileLocation = "drools-rules"
with a rule file located in a subdirectory:
~/my-grails-app/src/resources/drools-rules/packageOne/ruleFile1.drl
The rule file will be avaiable on the classpath as
drools-rules/packageOne/ruleFile1.drl
and the KieBase packages property would be:
packages: "drools-rules.packageOne"
The plugin offers three command-line scripts.
Running grails create-drools-config will copy the default DroolsConfig.groovy to your application's grails-app/conf directory.
Running grails create-drools-context will copy the default drools-context.xml to your application's grails-app/conf directory.
Running grails create-drools-config will create a domain class with a package and name of your choice. Use this class to store your rules in the database.
It will also add or update the configuration option below in your application's grails-app/conf/Config.groovy:
grails.plugin.drools.droolsRuleDomainClass = "com.example.DroolsRule"