Hibernate(四)一对多映射 补充三：双向多对一关系（学生-->班级)

数据库及其他文件见hibernate(四)一对多映射 补充一：单向一对多关系（班级->学生）

package com.imooc.entity;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

/**
* 班级
* @author Administrator
*
*/
public class Grade implements Serializable{
/**
*
*/
private static final long serialVersionUID = 1L;
private int gid;
private String gname;
private String gdesc;
//在一方定义一个多方的集合
private Set<Student> students = new HashSet<Student>();

public Grade() {
super();
}

public Grade(String gname, String gdesc) {
super();
this.gname = gname;
this.gdesc = gdesc;
}

public Grade(int gid, String gname, String gdesc, Set<Student> students) {
super();
this.gid = gid;
this.gname = gname;
this.gdesc = gdesc;
}
public int getGid() {
return gid;
}
public void setGid(int gid) {
this.gid = gid;
}
public String getGname() {
return gname;
}
public void setGname(String gname) {
this.gname = gname;
}
public String getGdesc() {
return gdesc;
}
public void setGdesc(String gdesc) {
this.gdesc = gdesc;
}
public Set<Student> getStudents() {
return students;
}
public void setStudents(Set<Student> students) {
this.students = students;
}

}

<?xml version="1.0"?>
<!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.imooc.entity.Grade" table="grade" >
<id name="gid" column="gid" type="java.lang.Integer">
<generator class="increment"></generator><!--increment Hibernate自增  -->
</id>
<property name="gname" type="java.lang.String">
<column name="gname" length="20" not-null="true"></column>
</property>
<property name="gdesc" >
<column name="gdesc"></column>
</property>
<set name="students" table="student">
<key column="gid"></key>
<one-to-many class="com.imooc.entity.Student"/>
</set>
</class>

</hibernate-mapping>

package com.imooc.entity;

/**
* 学生
* @author Administrator
*
*/
public class Student {

public Student(String sname, String sex) {
super();
this.sname = sname;
this.sex = sex;
}

public Student() {
super();
}

private int sid;
private String sname;
private String sex;
private Grade grade;
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 getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}

public Grade getGrade() {
return grade;
}

public void setGrade(Grade grade) {
this.grade = grade;
}

}

<?xml version="1.0"?>
<!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.imooc.entity.Student" table="student" >
<id name="sid" column="sid" type="java.lang.Integer">
<generator class="increment"></generator><!--increment Hibernate自增  -->
</id>
<property name="sname" type="java.lang.String">
<column name="sname" length="20" not-null="true"></column>
</property>
<property name="sex" >
<column name="sex"></column>
</property>
<!-- 配置多对一关联关系 -->
<many-to-one name="grade" class="com.imooc.entity.Grade" column="gid"></many-to-one>
</class>

</hibernate-mapping>

package com.imooc.entity;

import java.util.Set;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.imooc.util.HibernateUtil;

/**
* 双向多对一关系（学生--》班级）
* @author Administrator
*
*/
public class Test {

public static void main(String[] args) {
add();
//findStudentsByGrade();
//update();
//delete();
}

//将学生添加到班级
public static void add(){
Grade g = new Grade("JAVA一班"," Java软件开发一班 ");
Student stu1 = new Student("张三","男");
Student stu2 = new Student("慕女神","女");
//设置关联关系
stu1.setGrade(g);
stu2.setGrade(g);

g.getStudents().add(stu1);
g.getStudents().add(stu2);

Session session = HibernateUtil.getSession();
Transaction tx =  session.beginTransaction();
//保存班级
session.save(g);
//保存学生
session.save(stu1);
session.save(stu2);

tx.commit();
HibernateUtil.closeSession(session);
}
}

/*console执行结果: 下面两条update是赘余的浪费性能，不需要去更新student的gid在student在已经设置。所以可以在one的一方set标签中添加inverse="true"，表示由多的一方负责维护关联关系。
Hibernate: select max(gid) from grade
Hibernate: select max(sid) from student
Hibernate: insert into grade (gname, gdesc, gid) values (?, ?, ?)
Hibernate: insert into student (sname, sex, gid, sid) values (?, ?, ?, ?)
Hibernate: insert into student (sname, sex, gid, sid) values (?, ?, ?, ?)
Hibernate: update student set gid=? where sid=?
Hibernate: update student set gid=? where sid=?
*/

优化一：修改在one的一方set标签中添加inverse=”true”

<?xml version="1.0"?>
<!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.imooc.entity.Grade" table="grade" >
<id name="gid" column="gid" type="java.lang.Integer">
<generator class="increment"></generator><!--increment Hibernate自增  -->
</id>
<property name="gname" type="java.lang.String">
<column name="gname" length="20" not-null="true"></column>
</property>
<property name="gdesc" >
<column name="gdesc"></column>
</property>
<!-- <set>节点的inverse属性指定关联关系的控制方向，默认由one方来维护
关联关系中，inverse="false"则为主动方，由主动方负责维护关联关系
在一对多关联中，只能设置one方的inverse为true，这将有助于性能的改善 -->
<set name="students" table="student" inverse="true">
<key column="gid"></key>
<one-to-many class="com.imooc.entity.Student"/>
</set>
</class>

</hibernate-mapping>

/*
console:执行结果为：

Hibernate: select max(gid) from grade
Hibernate: select max(sid) from student
Hibernate: insert into grade (gname, gdesc, gid) values (?, ?, ?)
Hibernate: insert into student (sname, sex, gid, sid) values (?, ?, ?, ?)
Hibernate: insert into student (sname, sex, gid, sid) values (?, ?, ?, ?)
*/

优化二：保存班级的时候级联保存学生信息

cascade属性

1.all 对所有的操作进行级联操作

2.save-update 执行保存和更新操作时进行级联操作

3.delete 执行删除时进行级联操作

4.none 对所有操作不进行级联操作

<?xml version="1.0"?>
<!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.imooc.entity.Grade" table="grade" >
<id name="gid" column="gid" type="java.lang.Integer">
<generator class="increment"></generator><!--increment Hibernate自增  -->
</id>
<property name="gname" type="java.lang.String">
<column name="gname" length="20" not-null="true"></column>
</property>
<property name="gdesc" >
<column name="gdesc"></column>
</property>
<!-- <set>节点的inverse属性指定关联关系的控制方向，默认由one方来维护
关联关系中，inverse="false"则为主动方，由主动方负责维护关联关系
在一对多关联中，只能设置one方的inverse为true，这将有助于性能的改善
cascade="save-update" 保存和更新时级联操作
-->
<set name="students" table="student" inverse="true" cascade="save-update">
<key column="gid"></key>
<one-to-many class="com.imooc.entity.Student"/>
</set>
</class>

</hibernate-mapping>

<?xml version="1.0"?>
<!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.imooc.entity.Student" table="student" >
<id name="sid" column="sid" type="java.lang.Integer">
<generator class="increment"></generator><!--increment Hibernate自增  -->
</id>
<property name="sname" type="java.lang.String">
<column name="sname" length="20" not-null="true"></column>
</property>
<property name="sex" >
<column name="sex"></column>
</property>
<!-- 配置多对一关联关系 cascade="all" 增删改查student级联操作grade-->
<many-to-one name="grade" class="com.imooc.entity.Grade" column="gid" cascade="all"></many-to-one>
</class>

</hibernate-mapping>

package com.imooc.entity;

import java.util.Set;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.imooc.util.HibernateUtil;

/**
* 双向多对一关系（学生--》班级）
* @author Administrator
*
*/
public class Test {

public static void main(String[] args) {
add();
//findStudentsByGrade();
//update();
//delete();
}

//将学生添加到班级
public static void add(){
Grade g = new Grade("JAVA一班"," Java软件开发一班 ");
Student stu1 = new Student("张三","男");
Student stu2 = new Student("慕女神","女");
//设置关联关系
stu1.setGrade(g);
stu2.setGrade(g);

g.getStudents().add(stu1);
g.getStudents().add(stu2);

Session session = HibernateUtil.getSession();
Transaction tx =  session.beginTransaction();
//保存班级时级联保存学生信息
session.save(g);

tx.commit();
HibernateUtil.closeSession(session);
}

//查询学生所在班级信息
public static void findGradeByStudent(){
Session session = HibernateUtil.getSession();
//学生信息
Student student = (Student) session.get(Student.class, 2);
System.out.println(student.getSid()+","+student.getSname());

//班级信息 配置级联关系后直接.出来
Grade grade = student.getGrade();
System.out.println(grade.getGid()+","+grade.getGname());
}
}

/*
console:执行结果：
Hibernate: select student0_.sid as sid1_1_0_, student0_.sname as sname2_1_0_, student0_.sex as sex3_1_0_, student0_.gid as gid4_1_0_ from student student0_ where student0_.sid=?
2,慕女神
Hibernate: select grade0_.gid as gid1_0_0_, grade0_.gname as gname2_0_0_, grade0_.gdesc as gdesc3_0_0_ from grade grade0_ where grade0_.gid=?
1,JAVA一班
*/