Neo4j Same Entity Relationship persistence issue

问题

Is is possible to pls advice me how to go about.. doing a Same Entity Relationship..

For ex. Entity(class Person) relatesTo Entity(class Person).

CODE:

@NodeEntity 
public class Person 
{ 
    @GraphId @GeneratedValue 
    private Long id; 

    @Indexed(indexType = IndexType.FULLTEXT, indexName = "searchByPersonName") 
    private String personName; 

    @Fetch @RelatedTo(type = "CONNECTS_TO", direction = Direction.BOTH) 
    private Set<ConnectedPersons> connectedPersons; 

    public ConnectedPersons connectsTo(Person endPerson, String connectionProperty) 
    {       
        ConnectedPersons connectedPersons = new ConnectedPersons(this, endPerson, connectionProperty); 
        this.connectedPersons.add(connectedPersons); //Null Pointer Here(connectedPersons is null)
        return connectedPersons; 
    }
}

CODE:

@RelationshipEntity(type = "CONNECTED_TO") 
public class ConnectedPersons{ 

@GraphId private Long id; 

@StartNode private Person startPerson; 

@EndNode private Person endPerson; 

private String connectionProperty; 

public ConnectedPersons() { } 

public ConnectedPersons(Person startPerson, Person endPerson, String connectionProperty) {             this.startPerson = startPerson; this.endPerson = endPerson; this.connectionProperty = connectionProperty; 
}

I am trying to have a Relationship to the same class.. i.e. Persons connected to the Person.. When I invoke a Junit test :

    Person one = new Person ("One"); 

Person two = new Person ("Two"); 

personService.save(one); //Works also when I use template.save(one)

personService.save(two); 

Iterable<Person> persons = personService.findAll(); 

for (Person person: persons) { 
System.out.println("Person Name : "+person.getPersonName()); 
} 

one.connectsTo(two, "Sample Connection"); 

template.save(one);

I get Null pointer when I try to do one.connectsTo(two, "Prop"); Please could you tell where am I going wrong?

Thanks in advance.

回答1:

One other thing besides the missing initialization of the Set is that the class ConnectedPersons is a @RelationshipEntity. But in your class Person you are using it with the @RelatedTo annotation as if it were a @NodeEntity. You should use the @RelatedToVia annotation in the Person class instead.

回答2:

You are getting null pointer exception in the below code because you haven't initialized the connectedPersons collection.

this.connectedPersons.add(connectedPersons); //Null Pointer Here(connectedPersons is null)

Initialize the collection as shown below

@Fetch @RelatedTo(type = "CONNECTS_TO", direction = Direction.BOTH) 
private Set<ConnectedPersons> connectedPersons=new HashSet<ConnectedPersons>();

来源：https://stackoverflow.com/questions/18413242/neo4j-same-entity-relationship-persistence-issue

标签

neo4j

spring-data

spring-data-neo4j