com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.Z93F725A07423FE1C889F448B33BootD21F:248B33BootD21F

Question

I have a couple one to many relationships in spring between my classes. And when i try to get all my data an error like infinite recursion, here is the whole error message.

at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:25) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719) ~[jackson-databind-2.9.6.jar:2.9.6]

i have 2 classes that are connected with each other with OneToMany Relationship

USER CLASS

public class User  {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;
    @OneToMany(mappedBy = "User")
    private List<Conversation> Conversation;

CONVERSATION CLASS

public class Conversation {
     @Id  @GeneratedValue(strategy = GenerationType.IDENTITY)
     private Long id;
     @ManyToOne
     @JoinColumn(name = "User_id")
     private User User;

Results screeshot

Results screeshot

I don't know why it happens, but maybe it is because of the relationship with the class Failure.

Repository Class

@Query(nativeQuery = true, value = "SELECT * FROM `conversation` WHERE 1")
public List<Conversation> findAllConv();

Controller class

 @Autowired
        private ConversationRepository conv;
        
        @GetMapping("/GetAllConversation")
        public List<Conversation> getAllConv()
        {
            return conv.findAllConv();
        }
    

Full Trace

2021-05-14 12:58:57.306 ERROR 1540 --- [nio-8020-exec-1] w.s.e.ErrorMvcAutoConfiguration$SpelView : Cannot render error page for request [/survey/GetAllConversation/] and exception [Could not write JSON: Infinite recursion (StackOverflowError); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) (through reference chain: org.club.entities.User_$$_jvstf65_b["conversation"]->org.hibernate.collection.internal.PersistentBag[0]->org.club.entities.Conversation["user"]-

Answer 1

When using relations in general, you can adjust the "fetch" and "cascade" type. Fetching means, if all entries related to the one you want to load are loaded as well while cascading relates to operations on the current entry being passed down to relating objects.

Edit1: I would suggest you try setting the fetch type to lazy at least for the Conversation class:

@ManyToOne(fetch = FetchType.LAZY)

Apart from that, I would suggest using repositories that inherit from CrudRepository so you can use derived queries.

Edit2: After seeing the stack trace the problem becomes clear. Jackson is trying to bind the Conversation object to JSON but encounters an endless loop because of the Conversation reference in the User class.

There are two ways to solve this. If you still want to insert the User object referenced by a Conversation you can add the @JsonIgnore Annotation.

@JsonIgnore
@OneToMany(mappedBy = "User")
private List<Conversation> Conversation; 

If you don't care about the user at all, then you could also add this to the user reference in the conversation object:

@JsonIgnore
@JoinColumn(name = "User_id")
private User User;

If you later encounter problems, you could also think about mapping the Conversation objects returned by your repository to specific data transfer objects which are specifically made for the JSON mapping.

Answer 2

Judgind by the stacktrace, and the data model the problem lies in the fact, that you have two way relationship between User and Converstaion classes.

User have a list of Conversation items, which then link back to the user. When serializing, this creates an infinite loop :

serialize user -> serialize his conversations -> serialize coversation.user -> serialize his conversations etc.

One way to avoid this is to annotate the User field in converstaion with @JsonIgnore , this way when serializing user, you'll get his conversations, but since the reference back will be ignored by Jackson, you won't get the error from the stacktrace.

The exception message is pretty clear here: Infinite recursion (StackOverflowError) (through reference chain: org.club.entities.User_$$_jvstf65_b["conversation"]->org.hibernate.collection.internal.PersistentBag[0]->org.club.entities.Conversation["user"]-