Play 框架，OneToOne 关系不起作用

### 解决 Play 框架中 OneToOne 关系不起作用的问题

java
// User 实体类
@Entity
public class User extends Model {
    @Id
    public Long id;
    public String username;
    
    @OneToOne(mappedBy = "user", cascade = CascadeType.ALL)
    public UserProfile profile;
    
    // 其他属性和方法...
}
// UserProfile 实体类
@Entity
public class UserProfile extends Model {
    @Id
    public Long id;
    public String fullName;
    
    @OneToOne
    public User user;
    
    // 其他属性和方法...
}