How to write customized query for third table of manytomany mapping-CodePudding

I have created the Friends table which have self join ManyToMany relation. Friends entity have List of Friends which result as third table for representing the ManyToMany relation.

public class Friends {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;
    private String name;
    @ManyToMany
    @JoinTable(
              name = "friends_list", 
              joinColumns = @JoinColumn(name = "friends_from"), 
              inverseJoinColumns = @JoinColumn(name = "friends_to"))
    private List<Friends> friends;
    
    
}

I want to create a query on joined table. I have created Query like

@Query(value="Select * from friends_list f where f.friends_from=:id", nativeQuery=true)
    public List<Friends> findFriendsById(@Param("id") Long id);

Now, It throws the below error when I raise request of creating the resource.

@RestController
public class FriendsController {
    @Autowired
    private FriendsService friendsService;
    
    @PostMapping("/friends")
    public Friends createFriends(@RequestBody Friends frnd)
    {
        return friendsService.createFriends(frnd);
    }
    
    @GetMapping("/friends/{id}/distance/{k}")
    public List<Friends> getFriendsAtDistanceK(@PathVariable("id") Long id,@PathVariable("k") int k)
    {
        return friendsService.getFriendsAtDistanceK(id, k);
    }
}

Request

{
    "id":1,
    "name":"sujeet",
    "friends":[
        {
            "friends_from":1,
            "friends_to":2
        }
    ]
}

I have already created two friends without list of friends. And I am trying to add friends with list of friends. But it is showing below error.

org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.learn.friends.entity.Friends
    at org.hibernate.engine.internal.ForeignKeys.getEntityIdentifierIfNotUnsaved(ForeignKeys.java:347) ~[hibernate-core-5.6.5.Final.jar:5.6.5.Final]

CodePudding user response：

Have you tried using @Cascade({ CascadeType.SAVE_UPDATE, CascadeType.MERGE, CascadeType.PERSIST}) annotation for this? The source to this solution is here