hibernate关联保存（一对多）

弄了几天，终于做出Hibernate的第一个关联保存的例子出来了，还跑去广州购书中心看了一个下午的书，
还是感谢网友的帮助，让我弄懂了inverse和cascade这两个属性的使用。

package com.test.ORM;

import java.util.Set;

public class Student {
private int sid ;
private String sname ;
private String sage ;
private Set book;//用来接收、获取Book的对应一端中的<set name="就是这个名字">
public int getSid() {
   return sid;
}
public void setSid(int sid) {
   this.sid = sid;
}
public String getSname() {
   return sname;
}
public void setSname(String sname) {
   this.sname = sname;
}
public String getSage() {
   return sage;
}
public void setSage(String sage) {
   this.sage = sage;
}
public Set getBook() {
   return book;
}
public void setBook(Set book) {
   this.book = book;
}
}

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.test.ORM.Student" table="student">
   <id name="sid" type="int" >
    <column name="sid" not-null="true"/>
    <generator class="increment"/>
   </id>
   <property name="sname" type="string">
    <column name="sname" not-null="true"/>
   </property>
   <property name="sage" type="string">
    <column name="sage" not-null="true"/>
   </property>
   <set name="book" table="book" inverse="false" cascade="all">//最重点的地方,inverse="false"表示双向关联，也就是关系由两端来控制.cascade="all"就是关联的级别，还有all就是说无论是一方所有的操作(sava、update、delete等）当然也有其他值的。另一方也跟这对应的改变。
    <key column="sid" />
    <one-to-many class="com.test.ORM.Book" />
   </set>
</class>
</hibernate-mapping>

package com.test.ORM;

public class Book {
private int bid ;
private String bname ;
private String bprice ;
private Student student;

public Student getStudent() {
   return student;
}
public void setStudent(Student student) {
   this.student = student;
}
public int getBid() {
   return bid;
}
public void setBid(int bid) {
   this.bid = bid;
}
public String getBname() {
   return bname;
}
public void setBname(String bname) {
   this.bname = bname;
}
public String getBprice() {
   return bprice;
}
public void setBprice(String bprice) {
   this.bprice = bprice;
}
}

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.test.ORM.Book" table="book">
   <id name="bid" type="integer">
    <column name="bid" not-null="true" />
    <generator class="increment"/>
   </id>
   <property name="bname">
    <column name="bname" sql-type="varchar(16)" not-null="true"/>
   </property>
   <property name="bprice">
    <column name="bprice" sql-type="varchar(16)" not-null="true"/>
   </property>
   <many-to-one name="student" class="com.test.ORM.Student" fetch="select">//用来介绍一方中的students，呵呵，对应Book类中的private Student student;
    <column name="sid" not-null="true"/>
   </many-to-one>
</class>
</hibernate-mapping>

package com.test;

import java.util.HashSet;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import com.test.ORM.Book;
import com.test.ORM.Student;

public class TestOneToMany {

/**
* @param 测试类
*/
public static void main(String[] args)throws Exception {
   SessionFactory sf;
   Session session;
   Configuration config=new Configuration();
   config.configure();
   sf=config.buildSessionFactory();
   session=sf.openSession();
   Transaction ts=session.beginTransaction();
   //new 两个对象，只要保存student，book就会自动保存了
   Student student=new Student();
   student.setSname("student2");
   student.setSage("sage2");
 
 
   Book book=new Book();
   book.setBname("bname2");
   book.setBprice("bprice2");
   book.setStudent(student);
 
   Set bookSet=new HashSet();
   bookSet.add(book);
   student.setBook(bookSet);
   session.save(student);
 
   ts.commit();
   session.flush();
 
   session.close();
}
}

要具体了解hibernate 还是去看下hibernate 的保存机制吧，包括OID,事务管理什么的

错误解析：

package com.test;

import java.util.HashSet;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import com.test.ORM.Book;
import com.test.ORM.Student;

public class TestOneToMany {

/**
* @param 测试类
*/
public static void main(String[] args)throws Exception {
   SessionFactory sf;
   Session session;
   Configuration config=new Configuration();
   config.configure();
   sf=config.buildSessionFactory();
   session=sf.openSession();
   Transaction ts=session.beginTransaction();
 
   Student student=new Student();
   student.setSname("student3");
   student.setSage("sage3");
 
   Book book=new Book();
   Set bookSet=new HashSet();
 
   for(int i=0;i<2;i++){
    book.setBname("bname"+(2+i));
    book.setBprice("bprice"+(2+i));
    bookSet.add(book);
    System.out.println(i);
   }
   student.setBook(bookSet);
   session.save(student);
 
   ts.commit();
   session.flush();
 
   session.close();
}
}

//Hibernate: select max(sid) from student
//Hibernate: select max(bid) from book
//Hibernate: insert into student (sname, sage, sid) values (?, ?, ?)
//Hibernate: insert into book (bname, bprice, sid, bid) values (?, ?, ?, ?)
//Hibernate: update book set sid=? where bid=?
//先插入student，然后插入book,再更新book中的sid,但如果你的sid不能为空not-null="true"的话，那么在插入book的时候就会出现异常了