Mybatis实现单表增删改查操作

mybatis是对持久层进行了封装、mybatis文档地址：https://mybatis.org/mybatis-3/zh/index.html

下面实现单表的增删改查操作。

1.新建maven项目命名为mybatis、并在pom.xml中引入相关依赖

<?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.itheima</groupId>
    <artifactId>mybaits</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.6</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.12</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.10</version>
        </dependency>
    </dependencies>
</project>

2.数据库命名为eesy_mybatis,执行下列sql语句

DROP TABLE IF EXISTS `user`;

CREATE TABLE `user` (
  `id` int(11) NOT NULL auto_increment,
  `username` varchar(32) NOT NULL COMMENT '用户名称',
  `birthday` datetime default NULL COMMENT '生日',
  `sex` char(1) default NULL COMMENT '性别',
  `address` varchar(256) default NULL COMMENT '地址',
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (41,'老王','2018-02-27 17:47:08','男','北京'),(42,'小二王','2018-03-02 15:09:37','女','北京金燕龙'),(43,'小二王','2018-03-04 11:34:34','女','北京金燕龙'),(45,'传智播客','2018-03-04 12:04:06','男','北京金燕龙'),(46,'老王','2018-03-07 17:37:26','男','北京'),(48,'小马宝莉','2018-03-08 11:44:00','女','北京修正');

3编写实体类User与QV，包目录结构如下

public class User implements Serializable {

    //实体属性与数据库字段一一对应
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;
    
   //getter/setter【已省略】  
}

public class QV {
    private User user;
    private List<Integer> ids;

    //getter/setter【已省略】  
}

4.编写接口UserDao,包目录结构如下：

package com.dao;

import com.domain.QV;
import com.domain.User;

import java.util.List;

public interface userDao {

    //查询所有用户
    List<User> findAll();

    //保存单个用户
    int saveUser(User user);

    //更新用户信息
    int updateUser(User user);

    //删除用户信息
    int deleteUser(int id);

    //根据用户姓名模糊查询用户
    List<User> findUserByName(String name);

    //
    List<User> findByQV(String name);

    //多条件查询
    List<User> findByUser(User user);

    //传入查询条件QV对多个ID进行范围查询
    List<User> findByIds(QV qv);
}

5.编写mybaits的主配置函数SqlMapConfig.xml(命名随意，此处如此命名),包目录结构如下

<?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">
<!-- mybatis的主配置文件 -->
<configuration>
    <!-- 配置环境 -->
    <environments default="mysql">
        <!-- 配置mysql的环境-->
        <environment id="mysql">
            <!-- 配置事务的类型-->
            <transactionManager type="JDBC"></transactionManager>
            <!-- 配置数据源（连接池） -->
            <dataSource type="POOLED">
                <!-- 配置连接数据库的4个基本信息 -->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/eesy_mybatis?useUnicode=true&amp;characterEncoding=utf8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

    <!-- 配置子配置文件位置 -->
    <!-- 映射位置一一对应，包括包目录结构-->
    <mappers>
        <mapper resource="com/dao/userDao.xml"/>
    </mappers>
</configuration>

6.编写子配置文件userDao.xml,包目录结构如下

<?xml version="1.0" encoding="UTF-8"?>
<!--mybaits头约束 -->
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- 配置映射，填写绝对路径 -->
<mapper namespace="com.dao.userDao">

    <!-- 了解的内容：抽取重复的sql语句-->
    <sql id="defaultUser">
        select * from user
    </sql>
    
    <!--配置查询所有用户-->
    <select id="findAll" resultType="com.domain.User">
        select * from user
    </select>

    <!--保存单个用户,属性需要与domain实体中的属性一一对应-->
    <insert id="saveUser" parameterType="com.domain.User">
       insert into user(username,address,sex,birthday)values(#{username},#{address},#{sex},#{birthday});
    </insert>

    <!--更新用户信息-->
    <update id="updateUser" parameterType="com.domain.User">
        update user set username=#{username},sex=#{sex} where id=#{id};
    </update>

    <!--删除用户-->
    <delete id="deleteUser">
       delete from user  where id=#{id};
    </delete>

    <!--模糊查询-->
    <select id="findUserByName" parameterType="String" resultType="com.domain.User">
       select * from user where username like #{username};
    </select>

    <!--参数为对象类型 -->
    <select id="findByQV" parameterType="String" resultType="com.domain.User">
        select * from user where username like #{user.username};
    </select>

    <!--多条件查询-->
    <select id="findByUser" parameterType="com.domain.User" resultType="com.domain.User">
        select * from user
        <where>
            <if test="username!=null and username != ''">
                and username like #{username}
            </if>
            <if test="sex!=null and sex != ''">
                and sex like #{sex}
            </if>
        </where>
    </select>
    
    <!--传入多个ID对用户进行范围查询-->
    <select id="findByIds" parameterType="com.domain.QV" resultType="com.domain.User">
        <include refid="defaultUser"></include>
        <where>
            <if test="ids != null and ids.size()>0">
                <foreach collection="ids" open="and id in (" close=")" item="id" separator=",">
                    #{id}
                </foreach>
            </if>
        </where>
    </select>
</mapper>

7.编写测试类

package com.dao;

import com.domain.QV;
import com.domain.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.io.InputStream;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

/**
 * @author admin
 * @version 1.0.0
 * @ClassName mybaits.java
 * @Description TODO
 * @createTime 2020年01月10日 15:48:00
 */
public class mybaits {

    private InputStream in;
    private SqlSession sqlSession;
    private userDao userDao;

    @Before//用于在测试方法执行之前执行
    public void init() throws Exception {
        //1.读取配置文件，生成字节输入流
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2.获取SqlSessionFactory
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        //3.获取SqlSession对象
        sqlSession = factory.openSession();
        //4.获取dao的代理对象
        userDao = sqlSession.getMapper(userDao.class);
    }

    @After//用于在测试方法执行之后执行
    public void destroy() throws Exception {
        //提交事务
        sqlSession.commit();
        //6.释放资源
        sqlSession.close();
        in.close();
    }

    @Test
    public void findAll(){
       List<User> list =  userDao.findAll();
       for(User u : list){
           System.out.println(u.toString());
       }
    }

    @Test
    public void save() {
        User user = new User();
        user.setUsername("modify User property");
        user.setAddress("北京市顺义区");
        user.setSex("男");
        user.setBirthday(new Date());
        //执行方法
        userDao.saveUser(user);
    }

    @Test
    public void update() {
        User user = new User();
        user.setId(51);
        user.setUsername("update UserName");
        user.setSex("女");
        //执行方法
        userDao.updateUser(user);
    }

    @Test
    public void delete() {
        User user = new User();
        user.setId(51);
        //执行方法
        userDao.deleteUser(user.getId());
    }

    @Test
    public void findByUserName() {
        //执行方法
        List<User> list = userDao.findUserByName("小%");
        for(User user:list){
            System.out.println(user.toString());
        }
    }

    @Test
    public void findByQV() {
        //执行方法
        List<User> list = userDao.findByQV("小%");
        for(User user:list){
            System.out.println(user.toString());
        }
    }

    //多条件查询
    @Test
    public void findByUser() {
        User user = new User();
        user.setUsername("小%");
        user.setSex("男");
        //执行方法
        List<User> list = userDao.findByUser(user);
        for(User u:list){
            System.out.println(u.toString());
        }
    }

    //多个ID进行范围查询
    @Test
    public void findByIds() {
        List<Integer> list = new ArrayList<Integer>();
        list.add(42);
        list.add(43);
        list.add(45);
        QV qv = new QV();
        qv.setIds(list);
        //执行方法
        List<User> users = userDao.findByIds(qv);
        for(User u:users){
            System.out.println(u.toString());
        }
    }
}

笔记：

无反射不框架，mybatis框架很多地方要求一一对应，按别人的规则来利用这种一一对应以及相应的getter/setter可帮助开发

动态SQL是mybatis的一大特点，上述简单使用了下,动态sql文档的说明：https://mybatis.org/mybatis-3/zh/dynamic-sql.html

尽量保证实体类的属性与数据库字段的列名一致，如果不一致需要自己在子配置文件中进行相关配置，用resultMap

 <!-- 配置 查询结果的列名和实体类的属性名的对应关系 -->
    <resultMap id="userMap" type="uSeR">
        <!-- 主键字段的对应 -->
        <id property="userId" column="id"></id>
        <!--非主键字段的对应-->
        <result property="userName" column="username"></result>
        <result property="userAddress" column="address"></result>
        <result property="userSex" column="sex"></result>
        <result property="userBirthday" column="birthday"></result>
    </resultMap>