Question

我正在使用带有Java（嵌入式驱动程序）的Neo4j OGM 2.0.4驱动程序。当我在会话中保存（项目）时，一切看起来都很好。 Hovewer当我想从数据库加载项目时我得到了这个例外：

16:01:23.182 [main] INFO  org.neo4j.ogm.service.DriverService - Using driver: org.neo4j.ogm.drivers.embedded.driver.EmbeddedDriver
16:01:24.768 [main] DEBUG org.neo4j.ogm.service.Components - Setting driver to: org.neo4j.ogm.drivers.embedded.driver.EmbeddedDriver
16:01:24.782 [main] WARN  org.neo4j.ogm.session.Neo4jSession - Thread 1: neo4jCMS.entity.Author is not an instance of a persistable class
16:01:24.782 [main] WARN  org.neo4j.ogm.session.Neo4jSession - Thread 1: neo4jCMS.entity.Author is not an instance of a persistable class
Saved
Exception in thread "main" java.lang.NullPointerException
    at org.neo4j.ogm.MetaData.entityType(MetaData.java:280)
    at org.neo4j.ogm.session.Neo4jSession.entityType(Neo4jSession.java:486)
    at org.neo4j.ogm.session.delegates.LoadByTypeDelegate.loadAll(LoadByTypeDelegate.java:60)
    at org.neo4j.ogm.session.delegates.LoadByTypeDelegate.loadAll(LoadByTypeDelegate.java:108)
    at org.neo4j.ogm.session.Neo4jSession.loadAll(Neo4jSession.java:152)
    at neo4jCMS.TestSite.run(TestSite.java:35)
    at neo4jCMS.Application.main(Application.java:20)

执行时：

Author author1 = new Author("Author no 1");
Author author2 = new Author("Author no 2");

session.save(author1);
session.save(author2);
System.out.println("Saved");

Iterable<Author> authors = session.loadAll(Author.class);
for (Author author : authors)
{
  System.out.println("Author: " + author.getName());
}

我的节点类是：

@NodeEntity
public class Author
{
  @GraphId
  private Long id;
  private String _name;

  public Author() { _name = "";}

  public Author(String name)
  {
    _name = name;
  }

  public String getName()
  {
    return _name;
  }
}

Answer 1

首先，您需要在import string import random def target (): a = random.choice(string.digits) b = random.choice(string.digits) c = random.choice(string.digits) if a == b or a == c or c ==b or a == b == c: target(targt()) else: return str(a + b + c)类中添加一个无参数构造函数，以便OGM创建对象。

如果没有解决，请尝试再次重新运行loadAll代码段。我在第一次执行时看到了奇怪的异常。我认为这是固定的，但可能只在Author。

Answer 2

问题在于配置。新的SessionFactory（）没有参数＆＃34; myProject.subDirectory＆＃34;。添加后它可以正常工作。

使用OGM驱动程序从Neo4j数据库加载数据时出现NullPointerException

2 个答案: