Mybatis

Posted 2021-01-06 大道至简

Mybatis

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。

2、体验mybatis

1. 准备数据库和表

   mysql>create table users(id int primary key auto_increment , 
                            name varchar(20) , 
                            age int) ;

2. 创建模块引入maven依赖

   [pom.xml]

   <?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.oldboy</groupId>
     <artifactId>mybatis</artifactId>
     <version>1.0-SNAPSHOT</version>
   
     <dependencies>
       <!-- mysql驱动 -->
       <dependency>
         <groupId>mysql</groupId>
         <artifactId>mysql-connector-java</artifactId>
         <version>5.1.17</version>
       </dependency>
       <!--junit单元测试-->
       <dependency>
         <groupId>junit</groupId>
         <artifactId>junit</artifactId>
         <version>4.11</version>
       </dependency>
       <!-- mybatis类库 -->
       <dependency>
         <groupId>org.mybatis</groupId>
         <artifactId>mybatis</artifactId>
         <version>3.2.1</version>
       </dependency>
     </dependencies>
   </project>

3. 创建javabean

   /**
    * User类
    */
   public class User {
     private Integer id;
     private String name ;
     private int age ;
   
     //get//set
   }

4. 创建映射文件

   [resources/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" >
       insert into users(name,age) values(#{name},#{age})
     </insert>
   </mapper>

5. 创建配置文件

   [resources/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/big12"/>
       <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>
   

6. 编写测试类，实现插入

@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();

User u = new User() ;
u.setName("tom");
u.setAge(12);
//执行插入操作
sess.insert("users.insert" , u) ;
sess.commit();
sess.close();
}

3、实现mybatis的基本操作

3.1 update

1. 在映射文件中增加update语句

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

2. 调用session.update方法

   ...
   User u = new User() ;
   u.setName("tomas");
   u.setAge(22);
   u.setId(1);
   sess.update("users.update" , u) ;

3.2 select

3.2.1 查询一个

1. 映射文件增加查询语句

   [userMapper.xml]

   ...
   <select id="selectById" resultType="_User">
     select * from users where id = #{id}
   </select>
   ...

2. 配置文件添加别名

   [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>
     ...
     <typeAliases>
       <typeAlias type="com.oldboy.mybatis.domain.User" alias="_User"/>
     </typeAliases>
     ...
   </configuration>

   ?

3. API调用

   User u = sess.selectOne("users.selectById" , 1) ;

3.2.2 查询多个

1. 添加sql语句

   [userMapper.xml]

   ...
   <select id="selectAll" resultType="_User">
     select * from users
   </select>
   ...

2. API调用

   List<User> list = sess.selectList("users.selectAll" ) ;

3.3 delete

1. 添加sql语句

   [UserMapper.xml]

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

2. API调用

   sess.delete("users.delete" , 1) ;

4、获取数据库主键值

数据表如果主键是自动增长的话，如果要在程序插入时得到主键值可修改映射文件，具体如下：

[userMapper.xml]

<insert id="insert" useGeneratedKeys="true" keyProperty="id">
  ...
</insert>