标签：code class size duti 学生 java div gets 三生
提示；本文的操作是在入门一和二上面的
hibernate对映射类型
在开始是学习的时候，我以为一对多和多对一是同样的，后来发现不是这样，比如说班主任和班级里的学生，一个班级可能有多个学生，但是只有一个班主任，学生和班主任的关系是多对一，班主任和学生的关系是一对多，两者之间的区别在于它们的指向性
一对多（ont-to-many）和多对一（many-to-one）最常见和做常用的映射类型
1、创建班级表和学生表，通过外键进行关联（
alter table Students add constraint fk_students_gid foreign key (gid) references grade(gid);
）
2、创建班级表和学生表的实体类（属性/默认构造器、带参构造器、get和set方法，toString方法）
private int gid;
private String gname;
private String gdesc;
// 在一方定义一个多方的集合
private Set<Students> students = new HashSet<Students>();
//其他。。。略 }
public class Students {
private int sid;
private String sname;
private String gender;
private Date birthday;
//private String address;
private Blob pictur;
private Address address;
//其他。。。略
}
3、创建Grade.hbm.xml（我的Stuendt.hbm.xml已经配置好了）
<?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.hibernate.entity.Grade" table="grade">
<id name="gid" column="gid" type="int">
<generator class="increment"></generator>
</id>
<property name="gname" type="java.lang.String">
<column name="gname"/>
</property>
<property name="gdesc" type="java.lang.String">
<column name="gdesc"/>
</property>
<!--单项的一对多的关系-->
<set name="students" table="Students">
<!--指定的关联外键列-->
<key column="gid"></key>
<one-to-many class="com.hibernate.entity.Students"/>
</set>
</class>
</hibernate-mapping>
4、在cfg.xml中配置映射文件路径
<!--指定映射文件的路径-->
<mapping resource="com/hibernate/entity/Grade.hbm.xml"/>
<mapping resource="com/hibernate/entity/Students.hbm.xml"/>
5、创建HibernateUtil类
public class HibernadUtil {
private static SessionFactory sessionFactory;
private static Session session;
static {
StandardServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().configure().build();
sessionFactory = new MetadataSources(serviceRegistry).buildMetadata().buildSessionFactory();
}
//获取SessionFacory
public static SessionFactory getSessionFacory() {
return sessionFactory;
}
//获取session
public static Session getSession() {
return sessionFactory.openSession();
}
//关闭session
public static void closeSession(Session session) {
if (null != session) {
session.close();
}
}
6、进行测试
public class TestStudentsAndGrade {
public static void main(String[] args) {
//add();
//findStudensByGrade();
//update();
deleteStudentsBySid();
}
//给表中插入数据
public static void add() {
Grade grade = new Grade("道班", "道一");
Students s = new Students("道一", "男", new Date());
Students s2 = new Students("阴阳", "男", new Date());
Students s3 = new Students("三生", "女", new Date());
System.out.println(grade.getStudents().add(s));
//如果希望在学生表中添加对应道班级编号，需要在班级中添加学生，建立关联关系
grade.getStudents().add(s);
grade.getStudents().add(s2);
grade.getStudents().add(s3);
Session session = HibernadUtil.getSession();
//开启事务
Transaction transaction = session.beginTransaction();
session.save(grade);
session.save(s);
session.save(s2);
session.save(s3);
transaction.commit();
HibernadUtil.closeSession(session);
}
//查询班级中包含的学生
public static void findStudensByGrade() {
//获取session
Session session = HibernadUtil.getSession();
//获取班级信息
Grade grade = session.get(Grade.class, 1);
//输出班级信息
System.out.println(grade.getGname() + "," + grade.getGdesc());
//找出班级信息，然后找出班级学生信息
Set<Students> students = grade.getStudents();
for (Students stu:students
) {
System.out.println(stu);
}
}
//修改学生信息
public static void update(){
Grade grade =new Grade("道","道二");
Session session = HibernadUtil.getSession();
Transaction transaction = session.beginTransaction();
//修改学生所在班级信息（grade班级信息为自增长，别一不小心玩过头了）
Students students = session.get(Students.class, 2);
grade.getStudents().add(students);
session.save(grade);
transaction.commit();
HibernadUtil.closeSession(session);
}
//从班级中删除学生信息
public static void deleteStudentsBySid(){
Session session = HibernadUtil.getSession();
Transaction transaction = session.beginTransaction();
Students students = session.get(Students.class,9);
session.delete(students);
transaction.commit();
HibernadUtil.closeSession(session);
}
}
7、一对多中的set元素属性
标签：code class size duti 学生 java div gets 三生
原文地址：https://www.cnblogs.com/lindaiyu/p/10994131.html
