many-to-many-relationship between two entities in spring boot

Question

I have two Entities in my Spring-Boot Application:

User.java

@Entity
public class User {
      @Id
      @GeneratedValue(strategy = GenerationType.AUTO)
      Long id;
      String firstname;
      String lastname;
      String username;
      String password;
}

and

Role.java

Entity
@Table(name = "role")
public class Role {
      @Id
      @GeneratedValue(strategy = GenerationType.AUTO)
      Long id;
      String name;
      String description;
}

for my MySql database

I have excluded the getter and setter methods for this question.

I want to realise a Many-to-Many-Relationship between both Entities. Every user should be able to assign multiple roles to himself

I already Created a mapping table for both tables in my database. It has the rows

• user_id
• role_id.

I also created a new Entity UserRole.java which looks like this:

@Entity
@Table(name = "user_role")
public class UserRole implements Serializable{

    private User user;
    private Role role;

    @Id
    @ManyToOne
    @JoinColumn(name = "user_id")
    public User getuser() {
        return user;
    }

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

    @Id
    @ManyToOne
    @JoinColumn(name = "role_id")
    public Role getrole(){
        return role;
    }
    public void setRole(Role role){
        this.role = role;
    }

}

Now my question: is this construction correct? If yes, how do i add existing roles to an existing user and get the roles of this user in spring-boot?

Answer 1

You can find any tutorial connected with many-to-many relationship using Hibernate/Spring Data, example: Spring Data many-to-many

With your model it's simple to add the relationship mappings, like this:

@Entity
public class Role {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private String name;
    private String description;

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable
    private Set<User> users;
}

and this:

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private String firstname;
    private String lastname;
    private String username;
    private String password;

    @ManyToMany(mappedBy = "users")
    private Set<Role> roles;
}