Neo4J中无根据的关系

Question

I am using Spring Data Neo4J to define a undirected relationship between different persons. A sample entity class has been provided below.

@NodeEntity(label="Person")
public class Person {

    @GraphId
    private Long id;
    private String name;

    @Relationship(type = "FRIEND_WITH", direction=Relationship.UNDIRECTED)
    List<Person> friends;
}

As above, a Person has a list of friends of type "Person". The relationship is kept undirected to ensure that if a person A is "Friend_With" person B, then person B is also "Friend_With" Person A.

The code to add a friend is provided below

    if((person.getFriends() == null)||(person.getFriends().size()==0)){
        List<Person> friendList = new ArrayList<Person>();
        friendList.add(friend);
        person.setFriends(friendList);
    }else{
        person.getFriends().add(friend);
    }

    personRepository.save(person);

I have added PersonB as a friend of PersonA,so ideally, this should mean

PersonA - [:FRIEND_WITH] -> PersonB
PersonB - [:FRIEND_WITH] -> PersonA

as the relationship is undirected

But when I am querying, in Neo4J with

MATCH (p:Person)-[r:FRIEND_WITH]->(b:Person) where p.name = "PersonA" return p,b

I am getting the result as PersonA, PersonB. But when I am querying

MATCH (p:Person)-[r:FRIEND_WITH]->(b:Person) where p.name = "PersonB" 

no rows are returned. Thus the direction specified in the entity class does not seem to work. Also the Graph in Neo4J browser shows a directed edge from PersonA to PersonB.

All I want is that if PersonA is a friend of PersonB, the I will get the results, no matter, which way I ask. The code seems to work for

MATCH (p:Person)-[r:FRIEND_WITH]-(b:Person) where p.name = "PersonB" 

where the "->" is replaced by "-", but I do not want to use this.

What should I do ?

I am using spring-data-neo4j.version 4.0.0.RELEASE and spring-boot version spring-boot-starter-parent 1.3.0.M5

Answer 1

In Neo4j, ALL relationships are directed.

However, you can have the notion of undirected edges at query time. Just remove the direction from your MATCH query :

MATCH (p:Person)-[r:FRIEND_WITH]-(b:Person) where p.name = "PersonB" 

Why don't you want to use this ?