hibernate annotation 一对多保存对象时不能插入外键解决思路

@Entity@Table(name="TEACHERS")@SequenceGenerator(name="SEQ_TEACHERS",sequenceName="SEQ_TEACHERS")public class Teacher {        private Long id;        private String code;        private String name;        private String type;        private List<Student> students;        @Id    @GeneratedValue(generator="SEQ_TEACHERS",strategy=GenerationType.SEQUENCE)    @Column(name="id")    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }        @Column(name="CODE")    public String getCode() {        return code;    }    public void setCode(String code) {        this.code = code;    }        @Column(name="NAME")    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }        @Column(name="TYPE")    public String getType() {        return type;    }    public void setType(String type) {        this.type = type;    }        @OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER)    @JoinColumn(name="TECH_ID",nullable=true,updatable=true)    public List<Student> getStudents() {        return students;    }    public void setStudents(List<Student> students) {        this.students = students;    }}

@Entity@Table(name="STUDENTS")@SequenceGenerator(name="SEQ_STUDENTS",sequenceName="SEQ_STUDENTS")public class Student {        private Long id;        private String code;        private String name;//    @Column(name="TECH_ID")//    private Long techId;        private Teacher teacher;        @Id    @GeneratedValue(generator="SEQ_STUDENTS",strategy=GenerationType.SEQUENCE)    @Column(name="id")    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }        @Column(name="CODE")    public String getCode() {        return code;    }    public void setCode(String code) {        this.code = code;    }        @Column(name="NAME")    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    //    public Long getTechId() {//        return techId;//    }//    public void setTechId(Long techId) {//        this.techId = techId;//    }        @ManyToOne(cascade=CascadeType.ALL)    @JoinColumn(name="TECH_ID")    public Teacher getTeacher() {        return teacher;    }    public void setTeacher(Teacher teacher) {        this.teacher = teacher;    }}

public class AssociationsTest {    /**     * @param args     */    public static void main(String[] args) {//        SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();        SessionFactory sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();        Session session = sessionFactory.openSession();        Transaction trans = session.beginTransaction();        Teacher t = new Teacher();        t.setCode("000001");        t.setName("xiaoxue");        t.setType("shuxue");        List<Student> list = new ArrayList<Student>();        Student s0 = new Student();        s0.setCode("000001");        s0.setName("xioali");        list.add(s0);        Student s1 = new Student();        s1.setCode("000002");        s1.setName("zhangsan");        list.add(s1);        t.setStudents(list);        session.save(t);        trans.commit();    }}