[FIXED] Spring Arangodb stores edge but fail with MappingException: Couldn't find PersistentEntity for type class java.lang.Object

Issue

Does anyone already have the same issue when arangtoDB edge collection was linking to different objects? and was able to use ArangoSpring driver to operate with this without any problem?

I have this edge

@Data
@Edge("link2User")
public class Link2User<T> {
  @Id
  private String key;

  @From
  private User user;

  @To
  private T to;

  @Getter @Setter private String data;
  ...
  public Link2User(final User user, final T to) {
    super();
    this.user = user;
    this.to = to;
  ...
}

than repository

@Component
public interface Link2UserRepository<T> extends ArangoRepository<Link2User<T>, String> {
}

and when I try call:

@Autowired
Link2UserRepository<Item> l2uRepository;

...

Link2User<Item> link1 = new Link2User<Item>( user, Item);
v2uRepository.save(link1 );

My link is stored into ArangoDB but I get error:

DOP. org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.data.mapping.MappingException: Couldn't find PersistentEntity for type class java.lang.Object!] with root cause
org.springframework.data.mapping.MappingException: Couldn't find PersistentEntity for type class java.lang.Object!

Solution

Due to type erasure, the library cannot detect at runtime the class of the generic field @To, therefore it cannot find the related persistent entity.

You can work around it by creating a class:

public class Link2UserOfItem extends Link2User<Item> {
    public Link2UserOfItem(final User user, final Item to) {
        super(user,to);
    }
}

And:

@Autowired
Link2UserRepository<Item> l2uRepository;

...

Link2User<Item> link1 = new Link2UserToItem( user, Item);
l2uRepository.save(link1 );

In this way Spring Data ArangoDB will save an additional type hint field ("_class": "<pkg>.Link2UserOfItem") and will use it on read to deserialize it.

Answered By - rashtao