本文摘自YSOcean的博客，感受很不错，怕丢了就写在我本身的博客里了，有一些是本身加的！
这个知识点适用于多表查询，通常结合着懒加载使用，避免影响效率！！html
一、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，而且更名为MyBatis 。2013年11月迁移到Github。java
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）。mysql
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 消除了几乎全部的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。spring
二、MyBatis 入门实例基于xml配置
①、建立MySQL数据库：mybatisDemo和表：personsql
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create database mybatisDemo;
use mybatisDemo;
create table person(pid
int
primary key AUTO_INCREMENT, pname varchar(
50
), page
int
);
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②、创建一个Java工程，并导入相应的jar包数据库
相应的 jar 包下载连接：http://pan.baidu.com/s/1skZM09Z 密码：nkt6apache
③、在 MyBatisDemo 工程中添加数据库配置文件 mybatis-configuration.xml，这一步按照本身项目框架结构进行自由配置！服务器
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<?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>
<!-- 能够配置多个运行环境，可是每一个 SqlSessionFactory 实例只能选择一个运行环境
1、development:开发模式
2、work：工做模式-->
<environments
default
=
"development"
>
<!--id属性必须和上面的
default
同样 -->
<environment id=
"development"
>
<!--事务管理器
1、JDBC：这个配置直接简单使用了 JDBC 的提交和回滚设置。它依赖于从数据源获得的链接来管理事务范围
2、MANAGED：这个配置几乎没作什么。它历来不提交或回滚一个链接。而它会让容器来管理事务的整个生命周期
好比 spring 或 JEE 应用服务器的上下文，默认状况下，它会关闭链接。然而一些容器并不但愿这样，
所以若是你须要从链接中中止它，就能够将 closeConnection 属性设置为
false
，好比：
<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 链接对象源 -->
<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>
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④、定义表所对应的实体类session
⑤、定义操做 person 表的sql映射文件personMapper.xmlmybatis
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<?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:惟一标识符，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 查询语句差很少，对于只有一个查询条件后面的 #{pid}表示占位符，里面不必定要写pid,写啥均可以，可是不要空着；若是有多个查询条件，则要写pojo类里面的属性 -->
select * from person where pid = #{pid}
</select>
<!-- 查询person 表全部数据 -->
<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>
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⑥、向 mybatis-configuration.xml 配置文件中注册 personMapper.xml 文件
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<mappers>
<!-- 注册personMapper.xml文件，
personMapper.xml位于com.ys.bean这个包下，因此resource写成com/ys/bean/personMapper.xml-->
<mapper resource=
"com/ys/bean/personMapper.xml"
/>
</mappers>
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以下图所示：
⑦、建立测试类
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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 表全部数据
@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();
//因为咱们设置了主键的自增加机制，故这里不须要手动设置 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();
}
}
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四、MyBatis 入门实例 一对一 基于xml配置
这里咱们以老师和班级为例，假设通常班级只能拥有有一个老师，一个老师只能带一个班级。
①、建立实体类
Teacher.java和Classes.java
②、在数据库中根据实体类建立相应的数据表
③、定义操做 Classes 表的sql映射文件classesMapper.xml
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<?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>
<!--
方式二：嵌套查询：经过执行另一个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 是上一个查询获得的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>
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说明：咱们这里一对一的关联操做，有两种方式：
一、使用嵌套结果映射来处理重复的联合结果的子集
二、经过执行另一个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
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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);
}
}
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四、MyBatis 入门实例 一对多，多对一 基于xml配置
这里咱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、创建学生和班级的实体类
Student.java
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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 +
"]"
;
}
}
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Classes.java
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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 +
"]"
;
}
}
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②、在数据库中根据实体类建立相应的数据表
③、多对一：定义操做 Classes 表的sql映射文件classesMapper.xml
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<?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>
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④、一对多：定义操做 Student 表的sql映射文件studentMapper.xml
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<?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>
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⑤、向 mybatis-configuration.xml 配置文件中注册 classesMapper.xml 、studentMapper.xml文件
⑥、编写测试类
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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查询班级全部的学生信息
@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());
}
}
|
五、MyBatis 入门实例 多对多 基于xml配置
这里咱们以 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、在数据库中创建相应的表
users 表
groups 表
二者之间的关联表users_groups表
②、创建对应的实体类
Users.java
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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 +
"]"
;
}
}
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Groups.java
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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 +
"]"
;
}
}
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Users_Groups.java
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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;
}
}
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③、多对多：定义操做 sql映射文件userMapper.xml
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<?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，查看该用户下的全部用户组信息 -->
<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>
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⑤、向 mybatis-configuration.xml 配置文件中注册 userMapper.xml文件
⑥、编写测试类
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//多对多：根据根据用户 id 查询全部的用户组信息
@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());
}
}
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④、定义表所对应的实体类
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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
+
"]"
;
}
}
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