BAEL-803: Backward Chaining with Drools - changefix (#3020)

drools/src/main/java/com/baeldung/drools/backward_chaining/BackwardChaining.java

@@ -0,0 +1,30 @@
+package com.baeldung.drools.backward_chaining;
+
+import org.kie.api.runtime.KieSession;
+
+import com.baeldung.drools.config.DroolsBeanFactory;
+import com.baeldung.drools.model.Fact;
+import com.baeldung.drools.model.Result;
+
+public class BackwardChaining {
+    public static void main(String[] args) {
+        Result result = new BackwardChaining().backwardChaining();
+        System.out.println(result.getValue());
+        result.getFacts()
+            .stream()
+            .forEach(System.out::println);
+    }
+
+    public Result backwardChaining() {
+        Result result = new Result();
+        KieSession ksession = new DroolsBeanFactory().getKieSession();
+        ksession.setGlobal("result", result);
+        ksession.insert(new Fact("Asia", "Planet Earth"));
+        ksession.insert(new Fact("China", "Asia"));
+        ksession.insert(new Fact("Great Wall of China", "China"));
+
+        ksession.fireAllRules();
+
+        return result;
+    }
+}

drools/src/main/java/com/baeldung/drools/config/DroolsBeanFactory.java

@@ -3,7 +3,6 @@ package com.baeldung.drools.config;
 import org.drools.decisiontable.DecisionTableProviderImpl;
 import org.kie.api.KieServices;
 import org.kie.api.builder.*;
-import org.kie.api.io.KieResources;
 import org.kie.api.io.Resource;
 import org.kie.api.runtime.KieContainer;
 import org.kie.api.runtime.KieSession;
@@ -22,7 +21,7 @@ public class DroolsBeanFactory {
 
     private  KieFileSystem getKieFileSystem() throws IOException{
         KieFileSystem kieFileSystem = kieServices.newKieFileSystem();
-        List<String> rules=Arrays.asList("SuggestApplicant.drl","Product_rules.xls");
+        List<String> rules=Arrays.asList("BackwardChaining.drl","SuggestApplicant.drl","Product_rules.xls");
         for(String rule:rules){
             kieFileSystem.write(ResourceFactory.newClassPathResource(rule));
         }
@@ -56,9 +55,11 @@ public class DroolsBeanFactory {
         getKieRepository();
         KieFileSystem kieFileSystem = kieServices.newKieFileSystem();
 
+        kieFileSystem.write(ResourceFactory.newClassPathResource("com/baeldung/drools/rules/BackwardChaining.drl"));
         kieFileSystem.write(ResourceFactory.newClassPathResource("com/baeldung/drools/rules/SuggestApplicant.drl"));
         kieFileSystem.write(ResourceFactory.newClassPathResource("com/baeldung/drools/rules/Product_rules.xls"));
-
+        
+        
         KieBuilder kb = kieServices.newKieBuilder(kieFileSystem);
         kb.buildAll();
         KieModule kieModule = kb.getKieModule();

drools/src/main/java/com/baeldung/drools/model/Fact.java

@@ -0,0 +1,69 @@
+package com.baeldung.drools.model;
+
+import org.kie.api.definition.type.Position;
+
+public class Fact {
+
+    @Position(0)
+    private String element;
+
+    @Position(1)
+    private String place;
+
+    public Fact(String element, String place) {
+        this.element = element;
+        this.place = place;
+    }
+
+    public String getElement() {
+        return element;
+    }
+
+    public void setElement(String element) {
+        this.element = element;
+    }
+
+    public String getPlace() {
+        return place;
+    }
+
+    public void setPlace(String place) {
+        this.place = place;
+    }
+
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = 1;
+        result = prime * result + ((element == null) ? 0 : element.hashCode());
+        result = prime * result + ((place == null) ? 0 : place.hashCode());
+        return result;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj)
+            return true;
+        if (obj == null)
+            return false;
+        if (getClass() != obj.getClass())
+            return false;
+        Fact other = (Fact) obj;
+        if (element == null) {
+            if (other.element != null)
+                return false;
+        } else if (!element.equals(other.element))
+            return false;
+        if (place == null) {
+            if (other.place != null)
+                return false;
+        } else if (!place.equals(other.place))
+            return false;
+        return true;
+    }
+
+    @Override
+    public String toString() {
+        return "Fact{" + "element='" + element + '\'' + ", place='" + place + '\'' + '}';
+    }
+}

drools/src/main/java/com/baeldung/drools/model/Result.java

@@ -0,0 +1,31 @@
+package com.baeldung.drools.model;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Result {
+    private String value;
+    private List<String> facts = new ArrayList<>();
+
+    public String getValue() {
+        return value;
+    }
+
+    public void setValue(String value) {
+        this.value = value;
+    }
+
+    public List<String> getFacts() {
+        return facts;
+    }
+
+    public void setFacts(List<String> facts) {
+        this.facts = facts;
+    }
+    
+    public void addFact(String fact) {
+        this.facts.add(fact);
+    }
+    
+    
+}

drools/src/main/resources/com/baeldung/drools/rules/BackwardChaining.drl

@@ -0,0 +1,27 @@
+package com.baeldung.drools.rules
+
+import com.baeldung.drools.model.Fact;
+
+global com.baeldung.drools.model.Result result;
+
+dialect  "mvel"
+
+query belongsTo(String x, String y)
+  Fact(x, y;)
+  or
+  (Fact(z, y;) and belongsTo(x, z;))
+end
+
+rule "Great Wall of China BELONGS TO Planet Earth"
+when
+    belongsTo("Great Wall of China", "Planet Earth";)
+then
+	result.setValue("Decision one taken: Great Wall of China BELONGS TO Planet Earth");
+end
+
+rule "print all facts"
+when
+    belongsTo(element, place;)
+then
+    result.addFact(element + " IS ELEMENT OF " + place);
+end

drools/src/test/java/com/baeldung/drools/backward_chaining/BackwardChainingTest.java

@@ -0,0 +1,36 @@
+package com.baeldung.drools.backward_chaining;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.kie.api.runtime.KieSession;
+
+import com.baeldung.drools.config.DroolsBeanFactory;
+import com.baeldung.drools.model.Fact;
+import com.baeldung.drools.model.Result;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class BackwardChainingTest {
+    private Result result;
+    private KieSession ksession;
+ 
+    @Before
+    public void before() {
+        result = new Result();
+        ksession = new DroolsBeanFactory().getKieSession();
+    }
+
+    @Test
+    public void whenWallOfChinaIsGiven_ThenItBelongsToPlanetEarth() {
+
+        ksession.setGlobal("result", result);
+        ksession.insert(new Fact("Asia", "Planet Earth"));
+        ksession.insert(new Fact("China", "Asia"));
+        ksession.insert(new Fact("Great Wall of China", "China"));
+
+        ksession.fireAllRules();
+        
+        // Assert Decision one
+        assertEquals(result.getValue(), "Decision one taken: Great Wall of China BELONGS TO Planet Earth");
+    }
+}