Question

I’m developing a web app with user accounts. I have three system roles and a couple of users. I’ve implemented it this way (simplified for better understanding):

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

        @Id
        private String id;

        @Column(name = User.COLUMN_LOGIN)
        private String login;

        @Column(name = User.COLUMN_PASSWORD)
        private String password;

        @ManyToMany(cascade = CascadeType.DETACH, fetch = FetchType.EAGER)
        @JoinTable(name = "role_to_user",
                joinColumns={@JoinColumn(name = "userId")},
                 inverseJoinColumns={@JoinColumn(name = "roleId")})
        private Set<Role> roles = new LinkedHashSet<Role>();
   }

   @Table(name = "role")
   public class Role {

        @Id
        private String id;

        @Column(name = Role.COLUMN_ROLETYPE)
        private int roletype;
   }

What is the best way to implement date of assignment the role to user and date of ending this assignment ? My thought is to add column startDate and endDate to binding table named role_to_user, but i dont know how to tell it to hibernate 🙂

Is this great idea or is there any better way to do that ?

Thanks, Ondrej

Answer 1

You are right in your design assumptions. Someone said that in real life many-to-many relationships are very rare. You need a third table/object, let’s call it `RoleAssignment’:

@Entity
@Table(name = "role_to_user")
public class RoleAssignment {

    @ManyToOne
    private User user;

    @ManyToOne
    private Role role;

    private Date startDate;

    private Date endDate;

}

Of course some adjustments need to be made in User class:

@ManyToMany()
private Set<RoleAssignment> roles = new HashSet<>();

Now you can navigate from User to Role and filter inactive roles in the meantime.