hibernate在做一对多关联时，保存一方的对象，报出不能插入外键的错误的解决方法

写这篇文章将自己的解决方法保存，好记性，不如烂博客，哈哈。我写了两个类Teacher、Student，其中Teacher是一方，Student是多方，它们的关系通过在student的表中的外键Tech_ID来维护的，要做的功能是在保存一方的同时能保存多方。先贴出正确的代码：

@Entity@Table(name="TEACHERS")@SequenceGenerator(name="SEQ_TEACHERS",sequenceName="SEQ_TEACHERS",allocationSize=1,initialValue=1)public class Teacher {private Long id;private String code;private String name;private String type;private Set<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(fetch=FetchType.EAGER,mappedBy="teacher",cascade=CascadeType.ALL)//@Cascade(value={CascadeType.SAVE_UPDATE})//@JoinColumn(name="TECH_ID")public Set<Student> getStudents() {return students;}public void setStudents(Set<Student> students) {this.students = students;}}

@Entity@Table(name="STUDENTS")@SequenceGenerator(name="SEQ_STUDENTS",sequenceName="SEQ_STUDENTS",allocationSize=1,initialValue=1)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@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");    Set<Student> list = new HashSet<Student>();    Student s0 = new Student();    s0.setCode("000001");    s0.setName("xioali");    s0.setTeacher(t);    list.add(s0);    Student s1 = new Student();    s1.setCode("000002");    s1.setName("zhangsan");    s1.setTeacher(t);    list.add(s1);    t.setStudents(list);    session.save(t);    trans.commit();}}

在写这个功能的时候遇到了不少的问题，真的是不写不知道，写了才知道问题多多啊，先将自己的测试结果贴出：

之前我在测试的时候没有把student的属性teacher赋值，加了以后就没有问题
测试：
1、当我把Cascade从java.persistence转换成hibernate特有的，这样没有影响

2、我将@OneToMany中的mappedby去掉以后，就有问题，报出teachers_students中间表不存在，这个问题一个是因为我的配置文件没有配置自动建表，貌似hibernate默认是通过建中间表来实现一对多的关联关系。

3、在一方(Teacher)中的student集合上的JoinColumn(name='tech_id'),同时将多方(Student)的teacher属性上的注解多去掉,则出现下面的错误:
Exception in thread "main" org.hibernate.MappingException: Could not determine type for: com.myHibernate.vo.Teacher, for columns: [org.hibernate.mapping.Column(teacher)]
 at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:266)
 at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:253)

 at org.hibernate.mapping.Property.isValid(Property.java:185)
 at org.hibernate.mapping.PersistentClass.validate(PersistentClass.java:440)
 at org.hibernate.mapping.RootClass.validate(RootClass.java:192)
 at org.hibernate.cfg.Configuration.validate(Configuration.java:1102)
 at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1287)
 at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:867)
 at com.myHibernate.test.AssociationsTest.main(AssociationsTest.java:21)

 

还可以看我的帖子了解情况：hibernate 一对多 帖子