Cannot add more than one relationship between nodes in neo4j

问题:

I am trying to model a social network with Neo4J. This requires a user can have multiple relationships with another user. When I try to persist these relationships, only one is stored. For example, this is the test unit I do:

@Test public void testFindConnections() {      Id id1 = new Id();     id1.setId("first-node");      Id id2 = new Id();     id2.setId("second-node");     idService.save(id2);      id1.connectedTo(id2, "first-rel");     id1.connectedTo(id2, "second-rel");      idService.save(id1);      for (Id im : idService.findAll()) {         System.out.println("-" + im.getId());         if (im.getConnections().size() > 0) {             for (ConnectionType ite : im.getConnections()) {                 System.out                         .println("--" + ite.getId() + " " + ite.getType());             }         }     } } 

This should output:

-first-node --0 first-rel --1 second-rel -second-node --0 first-rel --1 second-rel 

However, it outputs:

-first-node --0 first-rel -second-node --0 first-rel 

This is my node entity:

@NodeEntity public class Id {      @GraphId     Long nodeId;     @Indexed(unique = false)     String id;      @Fetch     @RelatedToVia(direction=Direction.BOTH)     Collection<ConnectionType> connections = new HashSet<ConnectionType>(); } 

And my relationship entity:

@RelationshipEntity(type = "CONNECTED_TO") public class ConnectionType {      @GraphId Long id;     @StartNode Id fromUser;     @EndNode Id toUser;      String type; } 

What could the problem be? Is there any other way to model several relationships between nodes?

回答1:

This is not a shortcoming of Neo4j, it is a restriction of Spring Data Neo4j.

Usually if you have different types of relationships it would make sense to actually choose different relationship-types too, and not use a relationship-property for this.

CONNECTED_TO is also pretty generic.

Id is also a pretty generic class, shouldn't that be User or something similar?

FRIEND COLLEAGUE etc would be more meaningful.

---

That said, if you want to stay on your model you can either use

template.createRelationshipBetween(entity1,entity2,type,properties,true)

The true stands for allow-duplicates.

Alternatively use two different target types for the 2 types of relationships and use

@RelatedTo(enforceTargetType=true)

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