Drools5 Community TrainingHands On Playing with Rules

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Hands On 1: Drools ExpertPlaying with Rules

Drools5 Community Trainingversion: 1.0-SNAPSHOT

Release Date: 09/05/2011Under The Creative Common License

Hands On 1: Drools Expert Playing with Rules

Drools5 Community Training Course by Mauricio "Salaboy" Salatino and Esteban Aliverti is licensed under a Creative Commons Attribution 3.0

Unported License.Based on a work at salaboy.wordpress.

com.Permissions beyond the scope of this

license may be available at http://salaboy.wordpress.com/.

Overview

● Drools Expert Examples○ Introduction examples○ Conditional elements examples○ Rules Attributes examples

Introduction Examples

● Project: drools5/01-DroolsExpert-Introduction● Test: SimpleRulesExampleTest.java● Rules: src/main/resources/rules/rules.drl● Kbuilder, Kbase and Ksession (createKSession() method)

○ Take a look at the addEventListener() method● DRL syntax in the rule file:

○ Take a look at the LHS○ Take a look at the RHS

● Rules activation and execution (you can activate the logger)

Introduction Examples

● Exercise○ Find a way to get "Warn when we have a POP songs and

Playlist" Rule activated but not fired.○ Find a way to get "Warn when we have a POP songs and

Playlist" Rule activated and fired.

Conditional Elements examples

● Project: drools5/02-DroolsExpert-ConditionalElements ● Simple Rules Example:

○ Test Class: SimpleRulesExampleTest.java

○ Rules: SimpleRules.drl

○ Conditional Elements on LHS○ from Conditional Element

● Advanced from Examples:○ Test Class: AdvancedFromRulesExampleTest.java

○ Rules: AdvancedFromRules.drl○ collect, accumulate, accumulate custom function, Using

Hibernate session in from CE

Conditional Elements Examples

● Exercise 1 ○ Replace "Add Playlists that contains songs with letter 'a'

in their titles to the list using the accumulate conditional elements defining init, action, reverse and result functions. i.e:

from accumulate( $s: Song() from $songs, init(), action(), reverse(), result() )

Conditional Elements examples

Solution: rule "Playlists that contains songs with letter 'a' in their titles."when $playlist: Playlist($songs: songs) $match: java.util.List(empty == false) from accumulate( $s: Song() from $songs, init( java.util.List result = new java.util.ArrayList();), action( if ($s.getTitle().contains("a")) result.add($s); ), result( result ) )then System.out.println("Playlist found: "+$playlist); for (int i=0; i<$match.size(); i++){ System.out.println("\t--"+$match.get(i)); }end

Conditional Elements examples

● Exercise 2○ Create a custom accumulate function to collect random

songs from a playlist.○ Copy the SongsWithALetterOnTheirTitlesFunction.java implementation

Conditional Elements Examples

● eval Example:○ Test Class: EvalRulesExampleTest.java

○ Rules: /rules/EvalRules.drl

○ use of eval in LHS

● exists Example:○ Test Class: ExistsRulesExampleTest.java

○ Rules: ExistsRules.drl

○ use of exists and not in the LHS

Conditional Elements Examples

● Exercise○ Replace "Warn when we have a Playlist longer than 9000

seconds" with an equivalent Rule without using eval

Conditional Elements Examples

Solution

rule "Playlist longer than 9000 seconds without eval"when$playlist: Playlist($songs: songs) AND $n : Number(intValue > 9000) from accumulate( $s : Song() from $songs, sum($s.getDuration()))thenSystem.out.println("We have found a Playlist longer than 9000 seconds");end

Rule Attributes examples

● Project: drools/03-DroolsExpert-RulesAttributes● Test Class: RuleAttributesExampleTest.java● Attributes:

○ salience○ no-loop:

■ Test: noLoop() Rules: /rules/NoLoopRules.drl

○ lock-on-active: ■ Test: lockOnActive() Rules: /rules/LockOnActiveRules.drl

○ agenda-group: ■ Test: agendaGroup() Rules: /rules/AgendaGroupRules.drl

  

Questions?

Enjoy! Questions and Feedback are always appreciated!

  

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