Question

是否可以建议我如何去做...做同样的实体关系..

对于前。实体（类Person）涉及实体（类Person）。

代码：

@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; 
    }
}

代码：

@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; 
}

我正在尝试与同一个班级建立关系..即连接到此人的人..当我调用Junit测试时：

    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);

当我尝试one.connectsTo(two, "Prop");时，我得到Null指针请问你能告诉我哪里出错了吗？

提前致谢。

Answer 1

您在以下代码中获得空指针异常，因为您尚未初始化connectedPersons集合。

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

初始化集合，如下所示

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

Answer 2

除了缺少初始化Set之外的另一件事是ConnectedPersons类是@RelationshipEntity。但是在你的类Person中，你正在使用@RelatedTo注释，就像它是@NodeEntity一样。您应该在Person类中使用@RelatedToVia批注。

Neo4j相同实体关系持久性问题

2 个答案: