Spring Data Neo4j #RelatedToVia error on save() - spring-data-neo4j

Question

I'm getting the following error when I try to save an entity which has a #RelatedToVia attribute:
org.springframework.dao.InvalidDataAccessApiUsageException: Null parameter, startNode=NodeImpl#1, endNode=null, type=DynamicRelationshipType[BPA_PROPOSITION]; nested exception is java.lang.IllegalArgumentException: Null parameter, startNode=NodeImpl#1, endNode=null, type=DynamicRelationshipType[BPA_PROPOSITION]
From the error description above it seems that my RelationshipEntity is missing the end node. However, and this is the worst part of the problem, this is not true because I get this error randomly.
Here is the scenario. I'm creating some really simple tests just to check my class mappings. I manually create the classes necessary for each test case and then I save them. As Spring Data "cascades" the persistence of the entities my only concern is to populate the entity under test with its primitive properties and related entities, save it and then retrieve it back to see if the data is there.
This worked well for my first few classes which do not have #RelatedToVia mappings, but not for the ones which use #RelatedToVia. Here are some excerpts from the code which uses #RelatedToVia.
#NodeEntity
public class BasicProbabilityAssignmentFunction {
#GraphId
private Long id;
#RelatedTo(type = RelTypeConstants.BPA_FRAME, direction = Direction.OUTGOING)
private FrameOfDiscernment frameOfDiscernment;
#RelatedToVia(type = RelTypeConstants.BPA_PROPOSITION, direction = Direction.OUTGOING, elementClass = Belief.class)
private Set<Belief> beliefs;
}
#RelationshipEntity
public class Belief {
#GraphId
private Long id;
#StartNode
private BasicProbabilityAssignmentFunction bpaFunction;
#EndNode
private Proposition proposition;
}
#NodeEntity
public class Proposition {
#GraphId
private Long id;
#RelatedTo(type= RelTypeConstants.PROPOSITION_HYPOTHESIS, direction= Direction.OUTGOING)
private Set<Hypothesis> hypotheses;
#RelatedTo(type = RelTypeConstants.FRAME_PROPOSITION, direction = Direction.INCOMING)
private FrameOfDiscernment frameOfDiscernment;
}
Plus, here is an image of the variables state in debbuging mode just before calling the BasicProbabilityAssignmentFunction repository save. Notice that the Belief entity is fully populated!
And also the code used for test:
//this just creates an instance with its attributes populated
BasicProbabilityAssignmentFunction bpaFunction = BasicMockFactory.createBpaFunction();
//this is where I get the error.
bpaFunction = bpaFunctionRepository.save(bpaFunction);
One further note! I managed to stop getting this error by saving all entities (e.g., Proposition, Hypothesis etc) related to BasicProbabilityAssignmentFunction before saving BasicProbabilityAssignmentFunction itself. Nevertheless, I'm not sure why this solved the problem.
Answering Michael comment: Michael, are you saying that the rel-type should be defined in the Belief class itself (instead of using the type property of the #RelatedToVia annotation) or otherwise I should use template.createRelationshipBetween? I tried to use the #RelationshipEntity type property, but the problem persisted. What worked was saving the relationship #EndNode (Proposition) before the #Startnode (BasicProbabilityAssignmentFunction). By doing this, the Belief relationship is created (saved) without problem when the BasicProbabilityAssignmentFunction is saved.

Answer 1

This problem is already known. Please have a look at the following links:
http://forum.springsource.org/showthread.php?124316-Spring-Data-Neo4j-NullPointerException-with-RelatedToVia
https://jira.springsource.org/browse/DATAGRAPH-216