Mybatis 学习笔记

可学习渠道  MYBATIS 入门教程

1. Mybatis 介绍

　　Mybatis 是 sqlmap 技术，对 JDBC 进行封装，将大量的 SQL 语句外部化。

　　平时我们都用JDBC访问数据库，除了需要自己写 SQL 之外，还必须操作 Connection，Statment， ResultSet  这些其实只是手段的辅助类。 不仅如此，访问不同的表，还会写很多雷同的代码，显得繁琐和枯燥。

　　那么用了 Mybatis 之后，只需要自己提供 SQL 语句，其他的工作，诸如建立连接，Statement， JDBC 相关异常处理等等都交给 Mybatis 去做了，那些重复性的工作 Mybatis 也给做掉了，我们只需要关注在增删改查等操作层面上，而把技术细节都封装在了我们看不见的地方。

2. Mybatis 使用流程

2.1 创建数据库和表

# 创建数据库，略

# 使用数据库
use database_name ; 

# 创建 user 表
create table users(id int primary key auto_increment , name varchar() , age int);

2.2 创建模块，添加 Maven 依赖

 <?xml version="1.0" encoding="UTF-8"?>
 <project xmlns="http://maven.apache.org/POM/4.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>

     <groupId>com.share</groupId>
     <artifactId>mybatis</artifactId>
     <version>1.0-SNAPSHOT</version>

     <dependencies>

         <!-- MySQL依赖 -->
         <dependency>
             <groupId>mysql</groupId>
             <artifactId>mysql-connector-java</artifactId>
             <version>5.1.17</version>
         </dependency>

         <!-- 单元测试依赖 -->
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
             <version>4.11</version>
         </dependency>

         <!-- mybatis依赖 -->
         <dependency>
             <groupId>org.mybatis</groupId>
             <artifactId>mybatis</artifactId>
             <version>3.2.1</version>
         </dependency>

     </dependencies>

 </project>

pom.xml

2.3 创建实体类 User

 public class User {

     private Integer id;
     private String name;
     private int age;

     public Integer getId() {
         return id;
     }

     public void setId(Integer id) {
         this.id = id;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public int getAge() {
         return age;
     }

     public void setAge(int age) {
         this.age = age;
     }
 }

2.4 创建映射文件

 <?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">
     <!-- 定义名字空间 -->
     <mapper namespace="users">
     <!-- 定义insert语句 ,获得生成的id字段-->
     <insert id="insert" >
         insert into users(name,age) values(#{name},#{age})
     </insert>
 </mapper>     

UserMapper.xml

2.5 创建配置文件

 <?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>
     <properties>
         <property name="driver" value="com.mysql.jdbc.Driver"/>
         <property name="url" value="jdbc:mysql://localhost:3306/database_name"/>
         <property name="username" value="root"/>
         <property name="password" value="root"/>
     </properties>

     <environments default="development">
         <environment id="development">
             <transactionManager type="JDBC"/>
             <dataSource type="POOLED">
             <property name="driver" value="${driver}"/>
             <property name="url" value="${url}"/>
             <property name="username" value="${username}"/>
             <property name="password" value="${password}"/>
             </dataSource>
         </environment>
     </environments>

     <mappers>
         <mapper resource="UserMapper.xml"/>
     </mappers>

 </configuration>    

mybatis-config.xml

2.6 测试

 /**
 * 测试 insert
 */
 @Test
 public void tastInsert() throws Exception {
     //加载配置文件
     InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
     //创建会话工厂(Builder 模式)
     SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(in);
     //开启会话，相当于连接
     SqlSession sess = sf.openSession();

     User u = new User();
     u.setName("sam");
     u.setAge(17);

     sess.insert("users.insert", u);
     sess.commit();
     sess.close();
     System.out.println("insert success !!!");
 }

3. CRUD

3.1 修改 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">
 <!-- 定义名字空间 -->
 <mapper namespace="users">
     <!-- 定义insert语句 ,获得生成的id字段-->
     <insert id="insert" useGeneratedKeys="true" keyProperty="id">
         insert into users(name,age) values(#{name},#{age})
     </insert>

     <update id="update">
         update users set name = #{name} , age = #{age} where id = #{id}
     </update>

     <delete id="delete">
         delete from users where id = #{id}
     </delete>

     <select id="selectById" resultMap="rmUser">
       SELECT
         u.id uid,
         u.name uname,
         u.age uage ,
         o.id oid ,
         o.orderno oorderno ,
         o.price oprice
       from
         users u left OUTER join orders o on o.cid = u.id
       WHERE
         u.id = #{id}
     </select>
     <select id="selectAll" resultType="_User">
       select * from users
     </select>
     <!-- 用户映射 -->
     <resultMap id="rmUser" type="_User">
         <id column="uid" property="id" />
         <result column="uname" property="name" />
         <result column="uage" property="age"/>
         <collection property="orders" ofType="_Order" column="uid">
             <id column="oid" property="id" />
             <result column="oorderno" property="orderNo" />
             <result column="oprice" property="price"/>
         </collection>
     </resultMap>
 </mapper>

UserMapper.xml

3.2 修改 mybatis-config.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>
     <properties>
         <property name="driver" value="com.mysql.jdbc.Driver"/>
         <property name="url" value="jdbc:mysql://localhost:3306/database_name?allowMultiQueries=true"/>
         <property name="username" value="root"/>
         <property name="password" value="123456"/>
     </properties>

     <!--添加别名-->
     <typeAliases>
         <typeAlias type="com.share.mybatis.domain.User" alias="_User"/>
     </typeAliases>

     <environments default="development">
         <environment id="development">
             <transactionManager type="JDBC"/>
             <dataSource type="POOLED">
                 <property name="driver" value="${driver}"/>
                 <property name="url" value="${url}"/>
                 <property name="username" value="${username}"/>
                 <property name="password" value="${password}"/>
             </dataSource>
         </environment>
     </environments>

     <mappers>
         <mapper resource="UserMapper.xml"/>
     </mappers>

 </configuration>

mybatis-config.xml

3.3 测试

 /**
      * 测试 insert
      */
     @Test
     public void tastInsert() throws Exception {
         //加载配置文件
         InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
         //创建会话工厂(Builder 模式)
         SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(in);
         //开启会话，相当于连接
         SqlSession sess = sf.openSession();

         Order o = new Order();
         o.setOrderNo("2");
         o.setPrice(160);
         o.setId(5);
         User user = new User();
         user.setId(5);
         o.setUser(user);

         sess.insert("orders.insert", o);
         sess.commit();
         sess.close();
         System.out.println("insert success !!!");
     }

     /**
      * 测试 update
      */
     @Test
     public void tastUpdate() throws Exception {
         //加载配置文件
         InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
         //创建会话工厂(Builder 模式)
         SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(in);
         //开启会话，相当于连接
         SqlSession sess = sf.openSession();

         User u = new User();
         u.setName("Amy");
         u.setAge(18);
         u.setId(2);

         sess.update("users.update", u);
         sess.commit();
         sess.close();
         System.out.println("update success !!!");
     }

     /**
      * 测试 delete
      */
     @Test
     public void tastDelete() throws Exception {
         //加载配置文件
         InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
         //创建会话工厂(Builder 模式)
         SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(in);
         //开启会话，相当于连接
         SqlSession sess = sf.openSession();

         User u = new User();
         u.setId(3);

         sess.delete("users.delete", u);
         sess.commit();
         sess.close();
         System.out.println("delete success !!!");
     }

     /**
      * 测试 SelectOne
      */
     @Test
     public void testSelectOne() throws IOException {
         //加载配置文件
         InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
         //创建会话工厂(builder模式)
         SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(in);
         //开启会话，相当于连接
         SqlSession sess = sf.openSession();
         User u = sess.selectOne("users.selectById", 5);
         sess.commit();
         System.out.println(u.getName());
         sess.close();
     }

     /**
      * 测试 SelectAll
      */
     @Test
     public void testSelectAll() throws IOException {
         //加载配置文件
         InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
         //创建会话工厂(builder模式)
         SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(in);
         //开启会话，相当于连接
         SqlSession sess = sf.openSession();
         List<User> list = sess.selectList("users.selectAll");
         sess.commit();
         System.out.println(list.size());
         sess.close();
     }

4. 一对一

4.1 说明

一对一的本质为：　多对一 + 唯一性约束

4.2 创建表，加外键和唯一约束

# 删除 wifes_fk 表
drop table if exists wifes_fk ;

# 删除 husbands_fk 表
drop table if exists husbands_fk ;

# 创建 husbands_fk 表
create table husbands_fk(id int primary key auto_increment, hname varchar()) ;

# 创建 wifes_fk 表
create table wifes_fk(id int primary key auto_increment, wname varchar() , hid int , foreign key (hid) references husbands_fk(id) , unique (hid)) ;

# 插入数据
insert into husbands_fk(hname) values('tomas') ;

# 插入数据
insert into wifes_fk(wname , hid) values('jerry' , ) ;

5. 一对多

待补充。。。

6. 多对一

待补充。。。

7. 多对多

7.1 准备表

# 创建教师表
create table teas(id int primary key auto_increment, tname varchar()) ;

# 创建学生表
create table stus(id int primary key auto_increment, sname varchar()) ;

# 创建链接表
create table links(tid int , sid int , primary key (tid,sid) , foreign key (tid) references teas (id) , foreign key (sid) references stus (id)) ;

7.2 创建类

　　Teacher.java

 import java.util.ArrayList;
 import java.util.List;

 /**
  * 教师类
  */
 public class Teacher {

     private Integer id;
     private String tname;
     private List<Student> stus = new ArrayList<Student>();

     /**
      * 方便关联关系
      */
     public void addStudents(Student... stus) {
         for (Student s : stus) {
             this.getStus().add(s);
             s.getTeas().add(this);
         }
     }

     public List<Student> getStus() {
         return stus;
     }

     public void setStus(List<Student> stus) {
         this.stus = stus;
     }

     public Integer getId() {
         return id;
     }

     public void setId(Integer id) {
         this.id = id;
     }

     public String getTname() {
         return tname;
     }

     public void setTname(String tname) {
         this.tname = tname;
     }
 }

Teacher.java

　　Student.java

 import java.util.ArrayList;
 import java.util.List;

 /**
  * 学生类
  */
 public class Student {

     private Integer id;
     private String sname;
     private List<Teacher> teas = new ArrayList<Teacher>() ;

     public List<Teacher> getTeas() {
         return teas;
     }

     public void setTeas(List<Teacher> teas) {
         this.teas = teas;
     }

     public Integer getId() {
         return id;
     }

     public void setId(Integer id) {
         this.id = id;
     }

     public String getSname() {
         return sname;
     }

     public void setSname(String sname) {
         this.sname = sname;
     }
 }

Student.class

7.3 映射文件

　　TeacherMapper.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">
 <!-- 定义名字空间 -->
 <mapper namespace="teas">
     <insert id="insert" useGeneratedKeys="true" keyProperty="id">
         insert into teas(tname) values(#{tname})
     </insert>

     <insert id="insertLink">
       <foreach collection="stus" item="s">
           insert into links(tid,sid) values(#{id} , #{s.id}) ;
       </foreach>
     </insert>

     <select id="selectOne" resultMap="rmTeacher">
         select
           t.id tid , t.tname ttname , s.id sid , s.sname ssname
         from
           teas t
           left outer join links l on l.tid = t.id
           left outer join stus s on l.sid = s.id
         WHERE
           t.id = #{id}
     </select>
     <resultMap id="rmTeacher" type="_Teacher">
         <id column="tid" property="id"/>
         <result column="ttname"  property="tname"/>
         <collection property="stus" ofType="_Student" column="tid">
             <id column="sid" property="id" />
             <result column="ssname" property="sname"/>
         </collection>
     </resultMap>
 </mapper>

TeacherMapper.xml

　　

　　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">
 <!-- 定义名字空间 -->
 <mapper namespace="stus">
     <insert id="insert" useGeneratedKeys="true" keyProperty="id">
         insert into stus(sname) values(#{sname})
     </insert>
 </mapper>

StudentMapper.xml

7.4 修改配置文件，允许执行多条语句

在  mybatis-config.xml   文件中的  properties  里的  url  中添加      ?allowMultiQueries=true"

允许执行多条语句

<property name="url" value="jdbc:mysql://localhost:3306/DataBase_Name?allowMultiQueries=true"/>

添加别名

<!--添加别名-->
<typeAliases>
    <typeAlias type="com.share.mybatis.domain.Student" alias="_Student"/>
    <typeAlias type="com.share.mybatis.domain.Teacher" alias="_Teacher"/>
</typeAliases>

指定 mappers

<mappers>
    <mapper resource="StudentMapper.xml"/>
    <mapper resource="TeacherMapper.xml"/>
</mappers>

7.5 执行插入

 public class More2More {
     @Test
     public void testInsert() throws IOException {
         //加载配置文件
         InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
         //创建会话工厂(Builder 模式)
         SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(in);
         //开启会话，相当于连接
         SqlSession sess = sf.openSession();

         //创建对象
         Teacher t1 = new Teacher();
         Teacher t2 = new Teacher();

         Student s1 = new Student();
         Student s2 = new Student();
         Student s3 = new Student();
         Student s4 = new Student();

         //设置关联
         t1.addStudents(s1, s2, s3);
         t2.addStudents(s2, s3, s4);

         sess.insert("teas.insert", t1);
         sess.insert("teas.insert", t2);

         sess.insert("stus.insert", s1);
         sess.insert("stus.insert", s2);
         sess.insert("stus.insert", s3);
         sess.insert("stus.insert", s4);

         //插入关系
         sess.insert("teas.insertLink", t1);
         sess.insert("teas.insertLink", t2);

         sess.commit();
         sess.close();
         System.out.println("ok");

     }
 }

More2More.java

7.6 查询教师

在 TeacherMapper.xml 中添加查询

 <?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">
 <!-- 定义名字空间 -->
 <mapper namespace="teas">
     <insert id="insert" useGeneratedKeys="true" keyProperty="id">
         insert into teas(tname) values(#{tname})
     </insert>

     <insert id="insertLink">
       <foreach collection="stus" item="s">
           insert into links(tid,sid) values(#{id} , #{s.id}) ;
       </foreach>
     </insert>

     <select id="selectOne" resultMap="rmTeacher">
         select
           t.id tid , t.tname ttname , s.id sid , s.sname ssname
         from
           teas t
           left outer join links l on l.tid = t.id
           left outer join stus s on l.sid = s.id
         WHERE
           t.id = #{id}
     </select>
     <resultMap id="rmTeacher" type="_Teacher">
         <id column="tid" property="id"/>
         <result column="ttname"  property="tname"/>
         <collection property="stus" ofType="_Student" column="tid">
             <id column="sid" property="id" />
             <result column="ssname" property="sname"/>
         </collection>
     </resultMap>
 </mapper>

TeacherMapper.xml

查询部分代码

@Test
public void testSelectOne() throws IOException {
    InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
    SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(in);
    SqlSession sess = sf.openSession();
    Teacher t = sess.selectOne("teas.selectOne" , );
    sess.commit();
    System.out.println("ok");
}