如何一次删除Hibernate JoinTable中的所有关联?

@Entity
public class Role {
  ...
  @ManyToMany
  @JoinTable( name = "user_has_role", joinColumns = { @JoinColumn( name = "role_fk" ) }, inverseJoinColumns = { @JoinColumn( name = "user_fk" ) } )
  private Set<User>           userCollection; 
  ...
}

@Entity
public class User {
  ...
  //bi-directional many-to-many association to Role
  @ManyToMany( mappedBy = "userCollection" )
  private Set<Role>        roleCollection;
  ...
}

em.createQuery( "DELETE Role" ).executeUpdate();

this answer

for ( ... )
{
    A a = aDao.getObject(aId);
    B b = bDao.getObject(bId);

    b.getAs().remove(a);
    a.getBs().remove(b);
    bDao.saveObject(b); 
}

有没有一种方法可以在不遍历所有数据的情况下一次删除JoinTable中的所有关联? 可能有一个特殊的HQL命令,比如 DELETE Role.user_has_role ?