title: Spring Data JPA (Hibernate) is not creating column as autoincrement
body: <p><strong>Why is this mapping unable to create the column id as autoincrement?</strong></p>
  
  <pre><code>@Entity(name = "user_role")
  public class UserRole {
      @Id
      @GeneratedValue(strategy = GenerationType.AUTO)
      @Column(name = "id", nullable = false, unique = true)
      private Long id;
  
      @OneToOne(cascade = CascadeType.MERGE, targetEntity = Role.class)
      @JoinColumn(name = "role_id")
      private Role role;
  
      @OneToOne(cascade = CascadeType.MERGE, targetEntity = User.class)
      @JoinColumn(name = "user_id")
      private User user;
  }
  </code></pre>
  
  <p>Thanks in advance!</p>