org.hibernate.QueryException: could not resolve property: dep_id of: pojo.Studen

public ArrayList getliststudent(String depname) {
ArrayList list=new ArrayList();
Session session = HibernateSessionFactory.getSession();
String hql="from Departments  d where d.depname='"+depname+"'";
List list1=session.createQuery(hql).list();
Departments depart=new Departments();
Iterator iter1=list1.iterator();
if(iter1.hasNext()){
depart=(Departments) iter1.next();
int id=depart.getDep_id();
String hql1="from Student stu where stu.dep_id='"+id+"'";
list= (ArrayList) session.createQuery(hql1).list();
      System.out.print(list.size());
}
return list;

}
注意:dep_id是外键