Spring One-To-Many relationship throws Exception : org.springframework.http.converter.HttpMessageNotWritableException

Question

I try to create a simple relationship between two entities with spring. There is one User entity that holds many profile entities.

User Entity

@Entity
public class User {

    @OneToMany(mappedBy = "user")
    private List<Profile> profiles;

    public List<Profile> getProfiles() {
        return profiles;
    }

    public void setProfiles(List<Profile> profiles) {
        this.profiles = profiles;
    }
}

Profile Entity

@Entity
public class Profile {

    @ManyToOne
    @JoinColumn(name = "user_id", nullable = false)
    private User user;

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }
}

When I try to find a profile with this.profileRepository.findById(id).get() inside a @RestController I get this error:

org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: failed to lazily initialize a collection of role: User.profiles, could not initialize proxy - no Session; nested exception is com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: User.profiles, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->User["profiles"])]
The server encountered an unexpected condition that prevented it from fulfilling the request.

Can anyone explain to me why this is not working? I followed this tutorial.

Answer 1

as Mandar said, you can resolve it by eager fetch. But if you don't want to fetch all I mean eager fetch, then you have to initialize them for lazy fetch like this to the related class, your Profile class:

@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
@Entity
public class Profile implements Serializable{
//
//
.. your other stuffs
}

Edit: also change your User entity like this:

@Entity
public class User implements Serializable{

    @OneToMany(mappedBy = "user")
    private List<Profile> profiles = new LinkedHashSet<Profile>();
//...other stufs..
.
.
}

Hope, this will help!