MyBatis 详解（一对一，一对多，多对多）
1、什么是MyBatis?
MyBatis 本是apache的一个开源项目iBatis, 2010年这个项目由apache software foundation 迁移到了google code，并且改名为MyBatis 。2013年11月迁移到Github。
iBATIS一词来源于“internet”和“abatis”的组合，是一个基于Java的持久层框架。iBATIS提供的持久层框架包括SQL Maps和Data Access Objects（DAO）。
MyBatis 是支持普通 SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis 消除了几乎所有的JDBC代码和参数的手工设置以及结果集的检索。MyBatis 使用简单的 XML或注解用于配置和原始映射，将接口和 Java 的POJOs（Plain Ordinary Java Objects，普通的 Java对象）映射成数据库中的记录。
2、MyBatis 入门实例基于xml配置
①、创建MySQL数据库：mybatisDemo和表：person
create database mybatisDemo;
use mybatisDemo;
create table person(pid int primary key AUTO_INCREMENT, pname varchar(50), page int);
②、建立一个Java工程，并导入相应的jar包
③、在 MyBatisDemo 工程中添加数据库配置文件 mybatis-configuration.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!-- 可以配置多个运行环境，但是每个 SqlSessionFactory 实例只能选择一个运行环境
一、development:开发模式
二、work：工作模式-->
<environments default="development">
<!--id属性必须和上面的default一样 -->
<environment id="development">
<!--事务管理器
一、JDBC：这个配置直接简单使用了 JDBC 的提交和回滚设置。它依赖于从数据源得到的连接来管理事务范围
二、MANAGED：这个配置几乎没做什么。它从来不提交或回滚一个连接。而它会让容器来管理事务的整个生命周期
比如 spring 或 JEE 应用服务器的上下文，默认情况下，它会关闭连接。然而一些容器并不希望这样，
因此如果你需要从连接中停止它，就可以将 closeConnection 属性设置为 false，比如：
<transactionManager type="MANAGED">
<property name="closeConnection" value="false"/>
</transactionManager>
-->
<transactionManager type="JDBC"/>
<!--dataSource 元素使用标准的 JDBC 数据源接口来配置 JDBC 连接对象源 -->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatisdemo"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
</configuration>
④、定义表所对应的实体类
package com.ys.bean;
public class Person {
private int pid;
private String pname;
private int page;
public int getPid() {
return pid;
}
public void setPid(int pid) {
this.pid = pid;
}
public String getPname() {
return pname;
}
public void setPname(String pname) {
this.pname = pname;
}
public int getPage() {
return page;
}
public void setPage(int page) {
this.page = page;
}
@Override
public String toString() {
return "Person [pid=" + pid + ", pname=" + pname + ", page=" + page
+ "]";
}
}
⑤、定义操作 person 表的sql映射文件personMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.ys.bean.personMapper">
<!-- 根据 pid 查询 person 表中的数据
id:唯一标识符，此文件中的id值不能重复
resultType:返回值类型，一条数据库记录也就对应实体类的一个对象
parameterType:参数类型，也就是查询条件的类型
-->
<select id="selectPersonById"
resultType="com.ys.bean.Person" parameterType="int">
<!-- 这里和普通的sql 查询语句差不多，对于只有一个查询条件后面的 #{pid}表示占位符，里面不一定要写pid,写啥都可以，但是不要空着；如果有多个查询条件，则要写pojo类里面的属性 -->
select * from person where pid = #{pid}
</select>
<!-- 查询person 表所有数据 -->
<select id="getAllPerson" resultType="com.ys.bean.Person">
select * from person
</select>
<!-- 根据id更新数据 -->
<update id="updatePersonById" parameterType="com.ys.bean.Person">
update person set pname=#{pname},page=#{page} where pid = #{pid}
</update>
<!-- 向 person 表插入一条数据 -->
<insert id="addPerson" parameterType="com.ys.bean.Person">
insert into person(pid,pname,page) values(#{pid},#{pname},#{page})
</insert>
<!-- 根据 pid 删除数据 -->
<delete id="deletePersonById" parameterType="Long">
delete from person where pid=#{pid}
</delete>
</mapper>
⑥、向 mybatis-configuration.xml 配置文件中注册 personMapper.xml 文件
<mappers>
<!-- 注册personMapper.xml文件，
personMapper.xml位于com.ys.bean这个包下，所以resource写成com/ys/bean/personMapper.xml-->
<mapper resource="com/ys/bean/personMapper.xml"/>
</mappers>
⑦、创建测试类
package com.ys.test;
import java.io.InputStream;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import com.ys.bean.Person;
public class MyBatisTest {
SqlSession session;
@Before
public void beforeLoadXML(){
//加载 mybatis 配置文件
InputStream inputStream = MyBatisTest.class.
getClassLoader().getResourceAsStream("mybatis-configuration.xml");
//构建sqlSession的工厂
SqlSessionFactory sqlSessionFactory =
new SqlSessionFactoryBuilder().build(inputStream);
//根据 sqlSessionFactory 产生 session
session = sqlSessionFactory.openSession();
}
//根据 pid 查询 person 表中的数据
@Test
public void testSelectById(){
//这个字符串有 personMapper.xml 文件中 两个部分构成
//<mapper namespace="com.ys.bean.personMapper"> 的 namespace 的值
//<select id="selectPersonById" > id 值
String statement = "com.ys.bean.personMapper"+".selectPersonById";
Person p = session.selectOne(statement, 1);
System.out.println(p);
session.close();
}
//查询person 表所有数据
@Test
public void testGetAllPerson(){
String statement = "com.ys.bean.personMapper.getAllPerson";
List<Person> listPerson = session.selectList(statement);
System.out.println(listPerson);
session.close();
}
//根据id更新数据
@Test
public void updateById(){
String statement = "com.ys.bean.personMapper.updatePersonById";
Person p = new Person();
p.setPid(1);
p.setPname("aaa");
p.setPage(11);
session.update(statement, p);
session.commit();
session.close();
}
//向 person 表插入一条数据
@Test
public void addPerson(){
String statement = "com.ys.bean.personMapper.addPerson";
Person p = new Person();
//由于我们设置了主键的自增长机制，故这里不需要手动设置 pid 的值
//p.setPid(1);
p.setPname("add");
p.setPage(11);
session.insert(statement, p);
session.commit();
session.close();
}
//根据 pid 删除person 表中的数据
@Test
public void deletePersonById(){
String statement = "com.ys.bean.personMapper.deletePersonById";
session.delete(statement, 1);
session.commit();
session.close();
}
}
3、MyBatis 入门实例注解配置
①、上面的前面四步都是一样的，但是第五步不一样，我们不需要创建 personMapper.xml 文件，首先在 src 目录下创建 personMapper.java 文件
package com.ys.annocation;
import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;
import com.ys.bean.Person;
public interface PersonMapper {
@Insert("insert into person(pid,pname,page) values(#{pid},#{pname},#{page})")
public int add(Person person);
@Select("select * from person where pid = #{pid}")
public Person getPerson(int pid);
@Update("update person set pname=#{pname},page=#{page} where pid = #{pid}")
public int updatePerson(Person preson);
@Delete("delete from person where pid=#{pid}")
public int deletePerson(int pid);
}
②、向 mybatis-configuration.xml 配置文件中注册 personMapper.xml 文件
③、编写测试类
@Test
public void testAnnocation(){
PersonMapper mapper = session.getMapper(PersonMapper.class);
Person p = new Person();
p.setPid(7);
p.setPname("abc");
p.setPage(11);
//调用增加方法
mapper.add(p);
//调用查询方法
Person p1 = mapper.getPerson(3);
System.out.println(p1);
//调用更新方法
p.setPage(100);
mapper.updatePerson(p);
//调用删除方法
mapper.deletePerson(7);
session.commit();
session.close();
}
4、MyBatis 入门实例 一对一 基于xml配置
这里我们以老师和班级为例，假设一般班级只能拥有有一个老师，一个老师只能带一个班级。
①、创建实体类
Teacher.java
package one.to.one;
public class Teacher {
private int tid;
private String tname;
private Classes classes;
public int getTid() {
return tid;
}
public void setTid(int tid) {
this.tid = tid;
}
public String getTname() {
return tname;
}
public void setTname(String tname) {
this.tname = tname;
}
public Classes getClasses() {
return classes;
}
public void setClasses(Classes classes) {
this.classes = classes;
}
@Override
public String toString() {
return "Teacher [tid=" + tid + ", tname=" + tname + ", classes=" + classes + "]";
}
}
Classes.java
package one.to.one;
public class Classes {
private int cid;
private String cname;
private Teacher teacher;
public int getCid() {
return cid;
}
public void setCid(int cid) {
this.cid = cid;
}
public String getCname() {
return cname;
}
public void setCname(String cname) {
this.cname = cname;
}
public Teacher getTeacher() {
return teacher;
}
public void setTeacher(Teacher teacher) {
this.teacher = teacher;
}
@Override
public String toString() {
return "Classes [cid=" + cid + ", cname=" + cname + ", teacher=" + teacher + "]";
}
}
②、在数据库中根据实体类创建相应的数据表
③、定义操作 Classes 表的sql映射文件classesMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="one.to.one.classesMapper">
<!--
方式一：嵌套结果：使用嵌套结果映射来处理重复的联合结果的子集
封装联表查询的数据(去除重复的数据)
select * from classes c, teacher t where c.tid=t.tid and c.tid=#{tid}
-->
<select id="getClasses" resultMap="getClassesMap" parameterType="int">
select * from classes c ,teacher t
where c.tid=t.tid and c.tid=#{tid}
</select>
<resultMap type="one.to.one.Classes" id="getClassesMap">
<id column="cid" property="cid"/>
<result column="cname" property="cname"/>
<association property="teacher" javaType="one.to.one.Teacher">
<id column="tid" property="tid"></id>
<result column="tname" property="tname"/>
</association>
</resultMap>
<!--
方式一：嵌套结果：使用嵌套结果映射来处理重复的联合结果的子集
封装联表查询的数据(去除重复的数据)
select * from teacher t,classes c where t.cid = c.cid and t.cid=#{cid}
-->
<select id="getTeacher" resultMap="getTeacherMap" parameterType="int">
select * from teacher t,classes c
where t.cid = c.cid and t.cid=#{cid}
</select>
<resultMap type="one.to.one.Teacher" id="getTeacherMap">
<id column="tid" property="tid"/>
<result column="tname" property="tname"/>
<association property="classes" javaType="one.to.one.Classes">
<id column="cid" property="cid"/>
<result column="cname" property="cname"/>
</association>
</resultMap>
<!--
方式二：嵌套查询：通过执行另外一个SQL映射语句来返回预期的复杂类型
SELECT * FROM classes WHERE cid=1;
SELECT * FROM teacher WHERE tid=1 //1 是上一个查询得到的tid的值
property:别名(属性名) column：列名 -->
<!-- 把teacher的字段设置进去 -->
<select id="getClasses2" resultMap="getClassesMap2">
select * from classes c where c.cid = #{cid}
</select>
<resultMap type="one.to.one.Classes" id="getClassesMap2">
<id column="cid" property="cid"/>
<result column="cname" property="cname"/>
<collection property="teacher" column="tid" select="getTeacherCollection">
</collection>
</resultMap>
<select id="getTeacherCollection" resultType="one.to.one.Teacher">
select tid tid,tname tname from teacher where tid=#{tid}
</select>
</mapper>
说明：我们这里一对一的关联操作，有两种方式：
1、使用嵌套结果映射来处理重复的联合结果的子集
2、通过执行另外一个SQL映射语句来返回预期的复杂类型
相关属性解释：
④、向 mybatis-configuration.xml 配置文件中注册 classesMapper.xml 文件
⑤、编写测试类
package one.to.one;
import java.io.InputStream;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import com.ys.test.MyBatisTest;
public class OneToOneTest {
SqlSession session;
@Before
public void beforeLoadXML(){
//加载 mybatis 配置文件
InputStream inputStream = MyBatisTest.class.
getClassLoader().getResourceAsStream("mybatis-configuration.xml");
//构建sqlSession的工厂
SqlSessionFactory sqlSessionFactory =
new SqlSessionFactoryBuilder().build(inputStream);
//根据 sqlSessionFactory 产生 session
session = sqlSessionFactory.openSession();
}
//一对一嵌套结果方式：根据教师id查询班级信息
@Test
public void testGetClasses(){
String statement = "one.to.one.classesMapper.getClasses";
Classes c = session.selectOne(statement, 1);
System.out.println(c);
}
//一对一嵌套结果方式：根据班级id查询教师信息
@Test
public void testGetTeacher(){
String statement = "one.to.one.classesMapper.getTeacher";
Teacher t = session.selectOne(statement, 1);
System.out.println(t);
}
//一对一嵌套查询方式：根据教师id查询班级信息
@Test
public void testGetClasses2(){
String statement = "one.to.one.classesMapper.getClasses2";
Classes c = session.selectOne(statement, 1);
System.out.println(c);
}
}
4、MyBatis 入门实例 一对多，多对一 基于xml配置
这里我们以班级和学生为例，一个班级里面对应多个学生，这是一对多；反过来，多个学生对应一个班级，这是多对一
①、建立学生和班级的实体类
Student.java
package one.to.many;
public class Student {
private int sid;
private String sname;
private Classes classes;
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 Classes getClasses() {
return classes;
}
public void setClasses(Classes classes) {
this.classes = classes;
}
@Override
public String toString() {
return "Student [sid=" + sid + ", sname=" + sname + ", classes=" + classes + "]";
}
}
Classes.java
package one.to.many;
import java.util.Set;
public class Classes {
private int cid;
private String cname;
private Set<Student> students;
public int getCid() {
return cid;
}
public void setCid(int cid) {
this.cid = cid;
}
public String getCname() {
return cname;
}
public void setCname(String cname) {
this.cname = cname;
}
public Set<Student> getStudents() {
return students;
}
public void setStudents(Set<Student> students) {
this.students = students;
}
@Override
public String toString() {
return "Classes [cid=" + cid + ", cname=" + cname + ", students=" + students + "]";
}
}
②、在数据库中根据实体类创建相应的数据表
③、多对一：定义操作 Classes 表的sql映射文件classesMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="one.to.many.classesMapper">
<select id="getClasses" resultMap="getClassesMap">
select * from classes c,student s where s.cid=c.cid and c.cid=#{cid}
</select>
<resultMap type="one.to.many.Classes" id="getClassesMap">
<id column="cid" property="cid"></id>
<result column="cname" property="cname"/>
<collection property="students" ofType="one.to.many.Student">
<id column="sid" property="sid"/>
<result column="sname" property="sname"/>
</collection>
</resultMap>
</mapper>
④、一对多：定义操作 Student 表的sql映射文件studentMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="many.to.one.studentMapper">
<select id="getStudents" resultMap="getStudentMap">
select * from classes c,student s where s.cid=c.cid and s.sid=#{sid}
</select>
<resultMap type="one.to.many.Student" id="getStudentMap">
<id column="sid" property="sid"></id>
<result column="sname" property="sname"/>
<association property="classes" javaType="one.to.many.Classes">
<id column="cid" property="cid"/>
<result column="cname" property="cname"/>
</association>
</resultMap>
</mapper>
⑤、向 mybatis-configuration.xml 配置文件中注册 classesMapper.xml 、studentMapper.xml文件
⑥、编写测试类
package one.to.many;
import java.io.InputStream;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import com.ys.test.MyBatisTest;
public class OneToManyTest {
SqlSession session;
@Before
public void beforeLoadXML(){
//加载 mybatis 配置文件
InputStream inputStream = MyBatisTest.class.
getClassLoader().getResourceAsStream("mybatis-configuration.xml");
//构建sqlSession的工厂
SqlSessionFactory sqlSessionFactory =
new SqlSessionFactoryBuilder().build(inputStream);
//根据 sqlSessionFactory 产生 session
session = sqlSessionFactory.openSession();
}
//一对多嵌套结果方式：根据班级id查询班级所有的学生信息
@Test
public void testGetClasses(){
String statement = "one.to.many.classesMapper.getClasses";
Classes c = session.selectOne(statement, 1);
System.out.println(c);
System.out.println(c.getStudents().size());
}
//多对一嵌套结果方式：根据学生id查询班级信息
@Test
public void testGetStudents(){
String statement = "many.to.one.studentMapper.getStudents";
Student s = session.selectOne(statement, 1);
System.out.println(s);
System.out.println(s.getClasses());
}
}
5、MyBatis 入门实例 多对多 基于xml配置
这里我们以 users 表和 groups 表为例，一个 users 可能加入多个 groups，而一个 groups 可能包含多个 users，故构成 多对多 的关联
①、在数据库中建立相应的表
users 表
groups 表
两者之间的关联表users_groups表
②、建立对应的实体类
Users.java
package many.to.many;
import java.util.Set;
public class Users {
private int uid;
private String uname;
private Set<Groups> groups;
public int getUid() {
return uid;
}
public void setUid(int uid) {
this.uid = uid;
}
public String getUname() {
return uname;
}
public void setUname(String uname) {
this.uname = uname;
}
public Set<Groups> getGroups() {
return groups;
}
public void setGroups(Set<Groups> groups) {
this.groups = groups;
}
@Override
public String toString() {
return "User [uid=" + uid + ", uname=" + uname + ", groups=" + groups + "]";
}
}
Groups.java
package many.to.many;
import java.util.Set;
public class Groups {
private int gid;
private String gname;
private Set<Users> users;
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 Set<Users> getUsers() {
return users;
}
public void setUsers(Set<Users> users) {
this.users = users;
}
@Override
public String toString() {
return "Group [gid=" + gid + ", gname=" + gname + ", users=" + users + "]";
}
}
Users_Groups.java
package many.to.many;
public class Users_Groups {
private Users user;
private Groups group;
public Users getUser() {
return user;
}
public void setUser(Users user) {
this.user = user;
}
public Groups getGroup() {
return group;
}
public void setGroup(Groups group) {
this.group = group;
}
}
③、多对多：定义操作 sql映射文件userMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="many.to.many.userMapper">
<!-- 给一个用户 id，查看该用户下的所有用户组信息 -->
<select id="getUsers" resultMap="getGroupMap">
select g.gid,g.gname from users_groups ug,groups g
where ug.group_id=g.gid and ug.user_id=#{uid}
</select>
<resultMap type="many.to.many.Groups" id="getGroupMap">
<id column="gid" property="gid"/>
<result column="gname" property="gname"/>
<collection property="users" ofType="many.to.many.Users">
<id column="uid" property="uid"/>
<result column="uname" property="uname"/>
</collection>
</resultMap>
</mapper>
⑤、向 mybatis-configuration.xml 配置文件中注册 userMapper.xml文件
⑥、编写测试类
//多对多：根据根据用户 id 查询所有的用户组信息
@Test
public void testGetGroups(){
String statement = "many.to.many.userMapper.getUsers";
List<Groups> listGroup = session.selectList(statement,1);
for(Groups g : listGroup){
System.out.println(g.toString());
}
}
