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