用MyBatis进行数据库的增删改查

前提是MyBatis环境部署好了，参考地址：

https://www.cnblogs.com/package-java/p/10316536.html

为了方便演示，我提前在数据库插入了数据方便查询

1. 创建新的数据库`tedu_ums`；
 
    CREATE DATABASE tedu_ums;
 
2. 在新数据库中创建数据表`t_user`，表中至少包含id, username, password, age, phone, email这6个属性；  
 
    USE tedu_ums;
 
    CREATE TABLE t_user (
        id INT AUTO_INCREMENT,
        username VARCHAR(20) UNIQUE NOT NULL,
        password VARCHAR(20) NOT NULL,
        age INT,
        phone VARCHAR(20),
        email VARCHAR(50),
        PRIMARY KEY(id)
    ) DEFAULT CHARSET=utf8;
 
3. 添加不少于10条数据；
 
    INSERT INTO t_user  
        (username, password, age, phone, email)  
    VALUES  
        ('root', '1234', 18, '13800138001', 'root@tedu.cn'),
        ('admin', '4567', 19, '13800138002', 'admin@tedu.cn'),
        ('jack', '1234', 20, '13800138003', 'jack@tedu.cn'),
        ('tom', '1234', 22, '13800138010', 'tom@tedu.cn'),
        ('jerry', '1234', 25, '13800138011', 'jerry@tedu.cn'),
        ('rose', '1234', 21, '13800138004', 'rose@tedu.cn'),
        ('mike', '1234', 22, '13800138005', 'mike@tedu.cn'),
        ('lily', '1234', 23, '13800138006', 'lily@tedu.cn'),
        ('lucy', '1234', 24, '13800138007', 'lucy@tedu.cn'),
        ('mary', '1234', 25, '13800138008', 'mary@tedu.cn'),
        ('alex', '1234', 26, '13800138009', 'alex@tedu.cn');
 
4. 查询所有数据；
 
    SELECT id,username,password,age,phone,email FROM t_user;

一、创建实体类

每张数据表都应该有1个对应的实体类，所以，创建`cn.tedu.mybatis.entity.User`类，属性的数量与类型请参考数据表的设计：

package cn.tedu.mybatis.entity;

public class User {
    private Integer id;
    private String username;
    private String password;
    private Integer age;
    private String phone;
    private String email;
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public String getPhone() {
        return phone;
    }
    public void setPhone(String phone) {
        this.phone = phone;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", username=" + username + ", password=" + password + ", age=" + age + ", phone="
                + phone + ", email=" + email + "]";
    }

}

二、创建接口，声明抽象方法

创建`cn.tedu.mybatis.mapper.UserMapper`接口，并在接口中声明“插入用户数据”的抽象方法：

package cn.tedu.mybatis.mapper;

import cn.tedu.mybatis.entity.User;

public interface UserMapper {
    Integer addnew(User user);//增
    User findById(Integer id);//查
    Integer updatenew(User user);//改
    Integer deletenew(Integer id);//删

}

关于抽象方法，在MyBatis中，执行的操作如果是增、删、改，返回值均使用`Integer`，表示受影响的行数；方法的名称可以自定义，只要不违反Java的命名规则即可，另外，不允许在接口中使用重载机制；参数也可以自定义，如果执行的是增加操作，参数应该是与数据表对应的实体类的类型。

三、配置接口所在的包并配置配置XML文件的位置与数据源

1、在MyBatis中，通过`MapperScannerConfigurer`类扫描持久层接口的，所以，应该在`spring-dao.xml`文件中进行配置：
 2、MyBatis通过`SqlSessionFactoryBean`获取数据源，并且扫描配置了SQL语句的XML文件，最终由MyBatis框架来执行SQL语句，所以，需要在`spring-dao.xml`中配置`SqlSessionFactoryBean`：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
    xmlns:jdbc="http://www.springframework.org/schema/jdbc" xmlns:jee="http://www.springframework.org/schema/jee"
    xmlns:tx="http://www.springframework.org/schema/tx" xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:util="http://www.springframework.org/schema/util"
    xmlns:jpa="http://www.springframework.org/schema/data/jpa"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd
        http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-3.2.xsd
        http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-3.2.xsd
        http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd
        http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.3.xsd
        http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.2.xsd
        http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd
        http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.2.xsd">
    <!-- 加载数据库的配置文件 -->
    <util:properties id="dbConfig" location="classpath:db.properties"></util:properties>
<!--     配置数据源 -->
<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
<property name="url" value="#{dbConfig.url}"></property>
<property name="driverClassName" value="#{dbConfig.driver}"></property>
<property name="username" value="#{dbConfig.username}"></property>
<property name="password" value="#{dbConfig.password}"></property>
<property name="initialSize" value="#{dbConfig.initialSize}"></property>
<property name="maxActive" value="#{dbConfig.maxActive}"></property>
</bean>
<!-- 扫描持久层接口 -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<!-- 配置接口文件所在的包 -->
<property name="basePackage" value="cn.tedu.mybatis.mapper"></property>
</bean>
<!-- 或取数据源 -->
<bean class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource"></property>
<property name="mapperLocations" value="classpath:mappers/*.xml"></property>
</bean>

</beans>

四、在XML中配置接口方法对应的SQL语句

在`src/main/resources`下创建名为`mappers`文件夹，创建名为UserMapper.xml的文件

根节点必须是`<mapper>`，且根节点的`namespace`表示对应的接口文件，然后，添加子节点，以对应接口中的抽象方法：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//ibatis.apache.org//DTD Mapper 3.0//EN"
 "http://ibatis.apache.org/dtd/ibatis-3-mapper.dtd">
<!-- 根节点必须是mapper -->
<!-- namespace对应的接口文件 -->
<mapper namespace="cn.tedu.mybatis.mapper.UserMapper">
    <!-- 根据执行的操作类型选择节点 -->
    <!-- id:对应的抽象方法的方法名 -->
    <!-- 值：#{}括号里面的是User的属性名 -->
    <insert id="addnew">
        INSERT INTO t_user(
        username,password,age,phone,email
        ) value(
        #{username},#{password},#{age},#{phone},#{email}
        )
    </insert>
    <select id="findById" resultType="cn.tedu.mybatis.entity.User">
        SELECT id,username,password,age,phone,email FROM t_user WHERE id=#{id}
    </select>
    <insert id="addnewone">
        INSERT INTO t_user(
        username,password,age,phone,email
        ) value(
        #{username},#{password},#{age},#{phone},#{email}
        )
    </insert>
    <update id="updatenew">
        UPDATE t_user SET
        username=#{username},
        password=#{password},
        age = #{age},
        phone = #{phone},
        email=#{email}
        WHERE
        id=#{id}
    </update>
    <delete id="deletenew">
        DELETE FROM t_user WHERE age=#{age}
    </delete>
</mapper>

五、在测试类中测试

package web;

import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import cn.tedu.mybatis.entity.User;
import cn.tedu.mybatis.mapper.UserMapper;

public class TestDemo01 {
    AbstractApplicationContext ac;
    UserMapper mapper;
    @Before
    public void doBefore() {
        ac = new ClassPathXmlApplicationContext("spring-dao.xml");
        mapper = ac.getBean("userMapper",UserMapper.class);//根据id或取对象
    }
    @After
    public void doafter() {
        ac.close();
    }
/*    测试插入*/
    @Test
    public void add() {
        User user = new User();
        user.setUsername("学海无崖");
        user.setPassword("12345600");
        Integer row = mapper.addnew(user);
        System.out.println("row:"+row);
    }
/*    测试查询*/
    @Test
    public void findById() {
        Integer id=8;
        User user = mapper.findById(id);
        System.out.println(user);
    }
/*    测试修改*/
    @Test
    public void updatenew() {
        User user = new User();
        user.setUsername("小珠佩琦");
        user.setPassword("5548");
        user.setAge(18);
        user.setEmail("44@qq.com");
        user.setPhone("448484");
        user.setId(6);
        Integer num = mapper.updatenew(user);
        System.out.println("num:"+num);
    }
/*    测试删除*/
    @Test
    public void deletenew() {
        Integer age = 60;
        Integer row = mapper.deletenew(age);
        System.out.println("row:"+row);
    }

}