Drools5 Community Training HandsOn 1 Drools DRL Syntax

Drools5 Community TrainingHands On Playing with Rules Sponsored by Plugtree

Hands On 1: Drools Expert Playing with Rules Drools5 Community Training version: 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 examplesSolution: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 ExamplesSolutionrule "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

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Drools5 Community Training HandsOn 1 Drools DRL Syntax

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