How to persist @ManyToMany relation - duplicate entry or detached entity

Question

I want to persist my entity with ManyToMany relation. But i have some problem during persisting process.

My entities :

@Entity
@Table(name = \"USER\"         


        

Answer 1

Duplication Reason: Id is autogenerated, so every time a new role is being created. Use in this way :

User

@Entity
@Table(name = "user")
public class User {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int user_Id;

@Column(name = "email")
private String email;

@Column(name = "firstname")
private String firstname; 

@Column(name = "lastname")
private String lastname;

@Column(name = "password")
private String password;

@Column(name = "active")
private int active;

@ManyToMany(cascade = CascadeType.MERGE, fetch = FetchType.EAGER)
@JoinTable(name="user_role", 
    joinColumns=@JoinColumn(name="user_Id"),
    inverseJoinColumns=@JoinColumn(name="role_Id"))
private Set roles  = new HashSet<>();
//Getter and Setter

Role

@Entity
@Table(name="roles")
public class Role {

 @Id
 @Column(name="role_Id")
 private int role_Id;

 @Column(name="role_name")
 private String role_name;

 @ManyToMany(mappedBy = "roles")
 private Set users= new HashSet<>();

Controller (Should have added it to Service)

 @PutMapping("/addEmp")
   public String addEmp(@RequestBody User user) {

    String pass=passencoder.encode(user.getPassword());
    user.setPassword(pass);
    List roles =rolerepo.findAll();
    for(Role role: roles) 
        System.out.println("Roles"+ role.getRole_name());
    //user.setRoles(new HashSet < > (rolerepo.findAll()));
    userrepo.save(user);


    return "User Created";
}

Output

Roles

User_Role

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