关系：事物之间相互作用、相互联系的状态。范围最大。
联系：在关系数据库中表示实体与实体之间的联系，1:1,1:n,m:n。
关联：表示对象之间的关系，既有数量性，又有方向性；动词：将对象之间通过某种方式联系起来。
映射：这里指java对象和数据库表的一种对应关系。动词：形成这种对应关系。
级联：有关系的双方中操作一方，另一方也将采取一些动作。
关联的联系种类
在不考虑关联的方向前提下，联系就是关系数据库中表示实体与实体之间的联系，1:1,1:n,m:n。
一对一联系（1：1）：如用户和身份证、一夫一妻
一对多联系（1：n）：如班级和学生
多对多联系（m：n）：如学生和选课
关联的方向
关联关系的方向可分为单向关联和双向关联。
双向关联的方向其实就不重要了，因为通过任一一方都可以维护彼此的关系。也就是说：在双向关联中一对多和多对一都是一样的。
利用Java Project项目演示试用Hibernate技术添加数据到数据库
1 建立项目之后首先呢肯定是需要导入相关的JAR包的
2 然后是创建实体类
package cn.itcast.hiberate.sh.domain;
public class Student {
private Long sid;
private String sname;
private String description;
public Long getSid() {
return sid;
}
public void setSid(Long sid) {
this.sid = sid;
}
public String getSname() {
return sname;
}
public void setSname(String sname) {
this.sname = sname;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
@Override
public String toString() {
return "Student [sid=" + sid + ", sname=" + sname + ", description="
+ description + "]";
}
}
package cn.itcast.hiberate.sh.domain;
import java.util.Set;
public class Classes {
private Long cid;
private String cname;
private String description;
private Set<Student> students;
public Long getCid() {
return cid;
}
public void setCid(Long cid) {
this.cid = cid;
}
public String getCname() {
return cname;
}
public void setCname(String cname) {
this.cname = cname;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public Set<Student> getStudents() {
return students;
}
@Override
public String toString() {
return "Classes [cid=" + cid + ", cname=" + cname + ", description="
+ description + ", students=" + students + "]";
}
public void setStudents(Set<Student> students) {
this.students = students;
}
}Student映射文件
<?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>
<!-- name的值代表的是一个实体 -->
<class name="cn.itcast.hiberate.sh.domain.Student">
<!-- id用于指定主键 column,主键在数据库表列 ， increment,主键自增 -->
<!-- length,指定长度 type,类型，也可以不写 -->
<id name="sid" length="5" type="java.lang.Long">
<generator class="increment"></generator>
</id>
<!-- 表示表中普通的属性 -->
<property name="sname" length="20" type="java.lang.String"></property>
<property name="description" length="100" type="java.lang.String"></property>
</class>
</hibernate-mapping>Class映射文件
<?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>
<!-- name的值代表的是一个实体 -->
<class name="cn.itcast.hiberate.sh.domain.Classes">
<!-- id用于指定主键 column,主键在数据库表列 ， increment,主键自增 -->
<!-- length,指定长度 type,类型，也可以不写 -->
<id name="cid" length="5" type="java.lang.Long">
<generator class="increment"></generator>
</id>
<!-- 表示表中普通的属性 -->
<property name="cname" length="20" type="java.lang.String"></property>
<property name="description" length="100" type="java.lang.String"></property>
<!-- set元素和实体类中的 private Set<Student> students; 相对应 -->
<!--
set元素对应类中的set集合
通过set元素使classes表与student表建立关联
key是通过外键的形式让两张表建立关联
one-to-many是通过类的形式让两个类建立关联
cascade 级联
save-update
1、当 保存班级的时候，对学生进行怎么样的操作
如果学生对象在数据库中没有对应的值，这个时候会执行save操作
如果学生对象在数据库中有对应的值，这个时候会执行update操作
delete
all
inverse 维护关系
true 不维护关系
false 维护关系
default false
-->
<set name="students" cascade="save-update">
<!--
key是用来描述外键
-->
<key column="cid"></key>
<one-to-many class="cn.itcast.hiberate.sh.domain.Student"/>
</set>
</class>
</hibernate-mapping>3 然后是配置文件 hibernate.cfg.xml
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<!--
一个session-factory只能连接一个数据库
-->
<session-factory>
<!--
数据库的用户名
-->
<property name="connection.username">root</property>
<!--
密码
-->
<property name="connection.password">root</property>
<!--
url
-->
<property name="connection.url">
jdbc:mysql://localhost:3306/itcast_sh_hibernate
</property>
<!--
作用：根据持久化类和映射文件生成表
validate
create-drop
create
update
-->
<property name="hbm2ddl.auto">update</property>
<!--
显示hibernate内部生成的sql语句
-->
<property name="show_sql">true</property>
<mapping resource="cn/itcast/hiberate/sh/domain/Classes.hbm.xml" />
<mapping resource="cn/itcast/hiberate/sh/domain/Student.hbm.xml" />
</session-factory>
</hibernate-configuration>4 hibernate创建 sessionfactory 的工具类
package cn.itcast.hibernate.sh.utils;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.junit.Before;
public class HibernateUtils {
public static SessionFactory sessionFactory;
public static String url;
// 需要在加载的时候就进行配置
@Before
public void init(){
// 创建 Configuration 对象
Configuration configuration = new Configuration();
// 加载配置文件
configuration.configure(url);
sessionFactory = configuration.buildSessionFactory();
}
}5 测试类 需要注意的是，hibernate 可以创建相对应的表，但是 数据库需要自己先创建好
package cn.itcast.hibernate.sh.test;
import java.util.HashSet;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;
import cn.itcast.hiberate.sh.domain.Classes;
import cn.itcast.hiberate.sh.domain.Student;
import cn.itcast.hibernate.sh.utils.HibernateUtils;
public class TestOneToMany extends HibernateUtils{
static{
url="/hibernate.cfg.xml";
}
// 建表
@Test
public void testCreateTable(){
}
// 创建一个班级
/**
* Hibernate: select max(cid) from Classes
Hibernate: insert into Classes (cname, description, cid) values (?, ?, ?)
*/
@Test
public void save_classes(){
Session session = sessionFactory.openSession();
// 除了查询之外的操作都需要使用事务
Transaction transaction = session.beginTransaction();
Classes classes = new Classes();
classes.setCname("峡谷1");
classes.setDescription("召唤师峡谷");
session.save(classes); // 将临时状态的对象转换成持久化状态
transaction.commit();
session.close();
}
// 创建一个学生
/**
* Hibernate: select max(sid) from Student
Hibernate: insert into Student (sname, description, sid) values (?, ?, ?)
*/
@Test
public void save_student(){
// session 的实质可以看为一个数据库连接
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Student student = new Student();
student.setSname("黑铁");
student.setDescription("菜");
session.save(student);
transaction.commit();
session.close();
}
// 创建一个班级的时候同事创建一个学生,级联同时维护关系所以student表的外键也有值了
/**
* Hibernate: select max(cid) from Classes
Hibernate: select max(sid) from Student
Hibernate: insert into Classes (cname, description, cid) values (?, ?, ?)
Hibernate: insert into Student (sname, description, sid) values (?, ?, ?)
Hibernate: update Student set cid=? where sid=?
*/
@Test
public void saveClasses_cacade_saveStudent(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classes classes = new Classes();
classes.setCname("峡谷2");
classes.setDescription("召唤师峡谷2");
Student student = new Student();
student.setSname("白银呢");
student.setDescription("还是菜");
Set<Student> students = new HashSet<Student>();
students.add(student);
classes.setStudents(students);
session.save(classes);
transaction.commit();
session.close();
}
// 存在一个班级，新建一个学生
/**
* Hibernate: select classes0_.cid as cid0_0_, classes0_.cname as cname0_0_,
* classes0_.description as descript3_0_0_ from Classes classes0_ where classes0_.cid=?
Hibernate: select students0_.cid as cid0_1_, students0_.sid as sid1_,
students0_.sid as sid1_0_, students0_.sname as sname1_0_, students0_.description as descript3_1_0_ from Student students0_ where students0_.cid=?
Hibernate: select max(sid) from Student
Hibernate: insert into Student (sname, description, sid) values (?, ?, ?)
Hibernate: update Student set cid=? where sid=?
*/
@Test
public void test_classes_saveStudent(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classes classes = (Classes) session.get(Classes.class, 4L);
Student student = new Student();
student.setSname("白白");
student.setDescription("有点菜");
// classes 是持久化状态 可以直接添加
classes.getStudents().add(student);
session.save(classes);
transaction.commit();
session.close();
}
// 存在一个学生，新建一个班级
/**
* Hibernate: select student0_.sid as sid1_0_, student0_.sname as sname1_0_,
* student0_.description as descript3_1_0_ from Student student0_ where student0_.sid=?
Hibernate: select max(cid) from Classes
Hibernate: insert into Classes (cname, description, cid) values (?, ?, ?)
Hibernate: update Student set cid=? where sid=?
*/
@Test
public void test_student_saveClasses(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Student student = (Student) session.get(Student.class, 1L);
Classes classes = new Classes();
classes.setCname("峡谷3");
classes.setDescription("召唤师峡谷3");
Set<Student> students = new HashSet<Student>();
students.add(student);
classes.setStudents(students);
// 临时状态的 classes 需要 save
session.save(classes);
transaction.commit();
session.close();
}
// 存在一个 班级和学生 ，将其建立连接
/**
* Hibernate: select classes0_.cid as cid0_0_, classes0_.cname as cname0_0_,
* classes0_.description as descript3_0_0_ from Classes classes0_ where classes0_.cid=?
Hibernate: select student0_.sid as sid1_0_, student0_.sname as sname1_0_,
student0_.description as descript3_1_0_ from Student student0_ where student0_.sid=?
Hibernate: select students0_.cid as cid0_1_, students0_.sid as sid1_, students0_.sid as sid1_0_,
students0_.sname as sname1_0_, students0_.description as descript3_1_0_
from Student students0_ where students0_.cid=?
Hibernate: update Student set cid=? where sid=?
*/
@Test
public void updateClasses_cascade_updateStudent(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classes classes = (Classes) session.get(Classes.class, 2L);
Student student = (Student) session.get(Student.class, 5L);
classes.getStudents().add(student);
transaction.commit();
session.close();
}
// 把一个学生从一个班级解除关系
/**
* Hibernate: select classes0_.cid as cid0_0_, classes0_.cname as cname0_0_,
* classes0_.description as descript3_0_0_ from Classes classes0_ where classes0_.cid=?
Hibernate: select students0_.cid as cid0_1_, students0_.sid as sid1_,
students0_.sid as sid1_0_, students0_.sname as sname1_0_, students0_.description
as descript3_1_0_ from Student students0_ where students0_.cid=?
Hibernate: update Student set cid=null where cid=? and sid=?
*/
@Test
public void test_release(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classes classes = (Classes) session.get(Classes.class, 2L);
Set<Student> students = classes.getStudents();
for(Student s : students){
if(s.getSid() == 5){
students.remove(s);
}
}
// 解除了学生5的关系
transaction.commit();
session.close();
}
// 解除一个班级下面的一些学生的关系
@Test
public void test_releaseR(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classes classes = (Classes) session.get(Classes.class, 2L);
Set<Student> students = classes.getStudents();
for(Student s : students){
students.remove(s);
}
// 解除了班级2下面的关系
transaction.commit();
session.close();
}
// 删除学生
/**
* Hibernate: select student0_.sid as sid1_0_, student0_.sname as sname1_0_,
* student0_.description as descript3_1_0_ from Student student0_ where student0_.sid=?
Hibernate: delete from Student where sid=?
*/
@Test
public void testDelete(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Student student = (Student) session.get(Student.class, 5L);
session.delete(student);
transaction.commit();
session.close();
}
// 删除班级
/**
* Hibernate: select classes0_.cid as cid0_0_, classes0_.cname as cname0_0_, classes0_.description as descript3_0_0_ from Classes classes0_ where classes0_.cid=?
Hibernate: update Student set cid=null where cid=?
Hibernate: delete from Classes where cid=?
删除班级的同时级联删除了 学生表中相应的外键
*/
@Test
public void test_deleteClasses(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classes classes = (Classes) session.get(Classes.class, 5L);
session.delete(classes);
transaction.commit();
session.close();
}
}用于记忆整理，欢迎各位大神来指点
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