Spring Boot many to many post method not updating data

问题

My User class looks like this :

@Data
@Entity
public class User {
    @Id
    Long userID;
    @ManyToMany(mappedBy = "admins")
    private List<ClassRoom> classRooms  = new ArrayList<>();
}

And my ClassRoom class like this :

@Data
@Entity
public class ClassRoom {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    Long classRoomID;
    @ManyToMany
    @JoinTable(name ="classroom_user",
            joinColumns = @JoinColumn(name = "classroom_id"),
            inverseJoinColumns = @JoinColumn(name = "user_id"))
    private List<User> admins = new ArrayList<>();
}

And in my UserController class, I have :

@PostMapping("user/{id}/c")
User addClassRoom(@PathVariable Long id,@RequestBody ClassRoom newClassRoom)
{
    logger.debug(repository.findById(id));
    return repository.findById(id)
            .map(user -> {
                user.getClassRooms().add(newClassRoom);
                user.setClassRooms(user.getClassRooms());
                return repository.save(user);
            })
            .orElseGet(() -> {
                return null;
            });
}

And I POST and empty JSON ({}) and I see no change in my users. The Classroom or an empty Classroom doesn't get added in the User.

What is the problem here? How can I resolve this ?

回答1:

Can you paste the logs, please? Is Hibernate doing any insert into your table? Has the database schema been created in the DB correctly? One thing I recommend you to do is to add a custom table name on the top of your User class, using annotations like so: @Table(name = "users"). In most SQL dialects user is a reserved keyword, hence it is recommended to always annotate User class a bit differently, so that Hibernate won't have any problems to create a table for that entity.

回答2:

user.getClassRooms().add(newClassRoom); is suffice, user.setClassRooms(user.getClassRooms()); not required.

You will have to perform cascade save operation.List all cascade types explicitly and don't use mappedBy, instead use joincolumns annotation.

回答3:

IMO you must find classRoom by its id from repository, if it's new, you must create a new entity and save it first. Then assign it to user and save it. The object you receive from the post method was not created by the entity manager.

来源：https://stackoverflow.com/questions/58258189/spring-boot-many-to-many-post-method-not-updating-data

标签

Spring

spring-boot

jpa

spring-data-jpa

many-to-many