GH-2317 - Move logic towards visited nodes instead of relationships.

Closes #2317

Author: meistermeier

src/main/java/org/springframework/data/neo4j/core/mapping/DefaultNeo4jPersistentEntity.java

@@ -547,34 +547,43 @@ public boolean containsPossibleCircles(Predicate<PropertyFilter.RelaxedPropertyP
 	private boolean calculatePossibleCircles(Predicate<PropertyFilter.RelaxedPropertyPath> includeField) {
 		Collection<RelationshipDescription> relationships = new HashSet<>(getRelationshipsInHierarchy(includeField));
 
-		Set<RelationshipDescription> processedRelationships = new HashSet<>();
 		for (RelationshipDescription relationship : relationships) {
 			PropertyFilter.RelaxedPropertyPath relaxedPropertyPath = PropertyFilter.RelaxedPropertyPath.withRootType(this.getUnderlyingClass());
 			if (!filterProperties(includeField, relationship, relaxedPropertyPath)) {
 				continue;
 			}
-			if (processedRelationships.contains(relationship)) {
+			// We don't look at the direction because we need to look for cycles based on the modelled relationship
+			// direction instead of the "real graph" directions
+			NodeDescription<?> targetNode = relationship.getTarget();
+			if (this.equals(targetNode)) {
 				return true;
 			}
-			processedRelationships.add(relationship);
 			String relationshipPropertiesPrefix = relationship.hasRelationshipProperties() ? "." + ((Neo4jPersistentEntity<?>) relationship.getRelationshipPropertiesEntity())
 					.getPersistentProperty(TargetNode.class).getFieldName() : "";
-			if (calculatePossibleCircles(relationship.getTarget(), processedRelationships, includeField, relaxedPropertyPath.append(relationship.getFieldName() + relationshipPropertiesPrefix))) {
+
+			// Branch out with the nodes already visited before
+			Set<NodeDescription<?>> visitedNodes = new HashSet<>();
+			visitedNodes.add(targetNode);
+			if (calculatePossibleCircles(targetNode, visitedNodes, includeField, relaxedPropertyPath.append(relationship.getFieldName() + relationshipPropertiesPrefix))) {
 				return true;
 			}
 		}
 		return false;
 	}
 
-	private boolean calculatePossibleCircles(NodeDescription<?> nodeDescription, Set<RelationshipDescription> processedRelationships, Predicate<PropertyFilter.RelaxedPropertyPath> includeField, PropertyFilter.RelaxedPropertyPath path) {
+	private boolean calculatePossibleCircles(NodeDescription<?> nodeDescription, Set<NodeDescription<?>> visitedNodes, Predicate<PropertyFilter.RelaxedPropertyPath> includeField, PropertyFilter.RelaxedPropertyPath path) {
 		Collection<RelationshipDescription> relationships = ((DefaultNeo4jPersistentEntity<?>) nodeDescription).getRelationshipsInHierarchy(includeField, path);
 
 		for (RelationshipDescription relationship : relationships) {
-			if (processedRelationships.contains(relationship)) {
+			NodeDescription<?> targetNode = relationship.getTarget();
+			if (visitedNodes.contains(targetNode)) {
 				return true;
 			}
-			processedRelationships.add(relationship);
-			if (calculatePossibleCircles(relationship.getTarget(), processedRelationships, includeField, path.append(relationship.getFieldName()))) {
+			visitedNodes.add(targetNode);
+
+			// Branch out again for the sub-tree with all previously visited nodes
+			Set<NodeDescription<?>> branchedVisitedNodes = new HashSet<>(visitedNodes);
+			if (calculatePossibleCircles(targetNode, branchedVisitedNodes, includeField, path.append(relationship.getFieldName()))) {
 				return true;
 			}
 		}