从很多关系中返回一个列表?

我用Netbeans生成了实体类,它们如下所示:

@Table(name = "users")
public class Users implements Serializable {
    @Id
    @Basic(optional = false)
    @Column(name = "user_name")
    private String userName;
    @JoinTable(name = "user_roles", joinColumns = {
        @JoinColumn(name = "user_name", referencedColumnName = "user_name")}, inverseJoinColumns = {
        @JoinColumn(name = "role_name", referencedColumnName = "role_name")})
    @ManyToMany(fetch = FetchType.LAZY)
    private Collection<Roles> rolesCollection;

@Table(name = "roles")
public class Roles implements Serializable {
    @Id
    @Basic(optional = false)
    @Column(name = "role_name")
    private String roleName;
    @ManyToMany(mappedBy = "rolesCollection", fetch = FetchType.LAZY)
    private Collection<Users> usersCollection;

更糟糕的是,我有自己的类,我想用它在JSF页面上显示结果。以下是当前查询:

Query query = em.createQuery("SELECT NEW UserListQueryObject"
        + "(u.userName, ...)"
        + " FROM Users u",
        UserListQueryObject.class);
List<UserListQueryObject> users = query.getResultList();

它适用于简单的属性和一对一的关系。但对很多人来说不是。我试着这样加入:

Query query = em.createQuery("SELECT NEW UserListQueryObject"
        + "(u.userName, ...., r.roleName)"
        + " FROM Users u JOIN u.rolesCollection r",
        UserListQueryObject.class);

... 但是运行时抱怨“r”附近的语法不好,还抱怨r.roleName。它想返回一个角色,但我需要一个用户的所有角色!

我也不是SQL专家,所以很可能解决方案很简单。。。还是在读了“专业jpa2…”这本书之后,我被卡住了。谢谢你的帮助。