ejb3 toplink jpa 1.0查询和id序列策略(ejb3 toplink jpa 1.0 querying and id sequence strategy)

 我有两个问题：假设我们有一个名为class的实体，另一个叫做student。 每个班级都有学生。 
 
public class Clas implements Serializable {
@Id
  @GeneratedValue(strategy=GenerationType.SEQUENCE)
private int id;
@OneToMany(cascade=CascadeType.ALL)
Collection<Student> students;
public clas(){
super();
}
 ..... getters and setters
}
 
 q1：我得到异常，由于序列策略没有要映射的字段，当添加任何其他列如String name时，它可以工作，但我不需要该字段我该怎么办？ 
 
 Q2。 ids是自动生成的，我想查询类c1中的所有学生，但我没有这个类的id，如何在不使用id的情况下获得这样的查询？ 或者如何获取数据库实体id来查询它？ 
 
 我使用mysql服务器glassfish v2.1 toplink jpa 1.0 
 
 谢谢 

I have 2 questions: suppose we have one entity named class and another called student. each class has onetomany students.
 
public class Clas implements Serializable {
@Id
  @GeneratedValue(strategy=GenerationType.SEQUENCE)
private int id;
@OneToMany(cascade=CascadeType.ALL)
Collection<Student> students;
public clas(){
super();
}
 ..... getters and setters
}
 
q1: i get the exception there are no fields to be mapped because of sequence strategy, when adding any other column like String name, it works, but i don't need that field what can i do ?
 
q2. the ids is autogenerated, and i want to query all students in class c1, but i don't has the id of this class, how to get such query without using id? or how to get database entity id to query on it ?
 
iam working with mysql server glassfish v2.1 toplink jpa 1.0
 
Thanks

原文：https://stackoverflow.com/questions/8635695