Generate correct match strings for Neo4j relationships (#621)

* Add test to check many-to-many queries are generated properly

* Generate correct match strings for Neo4j relationships

Author: guillermocalvo

grails-datastore-gorm-neo4j/src/main/groovy/org/grails/datastore/gorm/neo4j/CypherBuilder.java

@@ -73,7 +73,10 @@ public void setStartNode(String startNode) {
 
     public void addMatch(String match) {
         if(!matches.contains(match)) {
-            matches.add(match);
+            // Add empty match if the target entity is already defined
+            final String lastNode = match.substring(match.lastIndexOf('('));
+            final boolean alreadyDefined = matches.stream().anyMatch(m -> m.endsWith(lastNode));
+            matches.add(alreadyDefined ? "" : match);
         }
     }
 
@@ -174,6 +177,8 @@ public String build() {
         }
 
         for (String m : matches) {
+            // Skip empty matches
+            if (m.isEmpty()) continue;
             cypher.append(COMMAND_SEPARATOR).append(m);
         }
 

grails-datastore-gorm-neo4j/src/main/groovy/org/grails/datastore/gorm/neo4j/engine/Neo4jQuery.groovy

@@ -712,11 +712,18 @@ class Neo4jQuery extends Query {
             }
             else {
                 String targetNodeName = "m_${builder.getNextMatchNumber()}"
+                String nextPrefix = targetNodeName
+                String relationship = ""
                 Association association = (Association)aq.association
+                if (criterion.entity instanceof RelationshipPersistentEntity) {
+                    String type = (criterion.entity as RelationshipPersistentEntity).type()
+                    relationship = "$nextPrefix:$type"
+                    targetNodeName = "m_${builder.getNextMatchNumber() + 1}"
+                }
                 builder.addMatch(
-                    entity.formatAssociationPatternFromExisting(association, "", prefix, targetNodeName)
+                    entity.formatAssociationPatternFromExisting(association, relationship, prefix, targetNodeName)
                 )
-                def s = CRITERION_HANDLERS.get(aq.criteria.getClass()).handle(entity, aq.criteria, builder, targetNodeName)
+                def s = CRITERION_HANDLERS.get(aq.criteria.getClass()).handle(entity, aq.criteria, builder, nextPrefix)
                 return new CypherExpression(s)
             }
 

grails-datastore-gorm-neo4j/src/test/groovy/grails/gorm/tests/ManyToManyQuerySpec.groovy

@@ -0,0 +1,57 @@
+package grails.gorm.tests
+
+import grails.gorm.annotation.Entity
+import grails.neo4j.Relationship
+import grails.neo4j.mapping.MappingBuilder
+import spock.lang.Issue
+
+class ManyToManyQuerySpec extends GormDatastoreSpec {
+
+    @Override
+    List getDomainClasses() {
+        [TestA, TestB, TestC]
+    }
+
+    @Issue('309')
+    def "many-to-many relationships are queried correctly"() {
+        setup:
+        def a = new TestA(testA: "aaa").save(flush: true, failOnError: true)
+        def c = new TestC(testC: "ccc").save(flush: true, failOnError: true)
+        new TestB(from: a, to: c, testB: "bbb").save(flush: true, failOnError: true)
+
+        when:
+        def result = TestA.createCriteria().list {
+            ccc {
+                eq("testB", "bbb")
+                to {
+                    eq("testC", "ccc")
+                }
+            }
+        }
+
+        then:
+        result.size() == 1
+        result[0].testA == a.testA
+    }
+}
+
+@Entity
+class TestA {
+    String testA
+    static hasMany = [ccc: TestB]
+}
+
+@Entity
+class TestC {
+    String testC
+    static hasMany = [aaa: TestB]
+}
+
+@Entity
+class TestB implements Relationship<TestA, TestC> {
+    String testB
+    static mapping = MappingBuilder.relationship {
+        type "A_REL_C"
+        direction Direction.OUTGOING
+    }
+}