当我想更新 jpa 中的列表时,表格保持为空。完全没有错误。存在获取器和设置器,只是未在此处列出。
这是我的课:
public class User implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue
private int id;
@ManyToMany
private List<Course> courses;
}
public class Course implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue
private int id;
@ManyToMany(mappedBy="courses")
private List<User> users;
}
这里是我保存对象的方法:
public boolean addCourse(User user, Course course){
List<User> cas = new ArrayList<User>();
cas.add(user);
EntityManager em = getEntityManager();
try{
em.getTransaction().begin();
course.setUsers(cas);
em.getTransaction().commit();
em.clear();
return true;
} catch(Exception e) {
em.getTransaction().rollback();
return false;
}
}