查询所有数据

首先在数据库里新建一个表

-- 删除tb_brand表
drop table if exists tb_brand;
-- 创建tb_brand表
create table tb_brand
(
    -- id 主键
    id           int primary key auto_increment,
    -- 品牌名称
    brand_name   varchar(20),
    -- 企业名称
    company_name varchar(20),
    -- 排序字段
    ordered      int,
    -- 描述信息
    description  varchar(100),
    -- 状态：0：禁用  1：启用
    status       int
);
-- 添加数据
insert into tb_brand (brand_name, company_name, ordered, description, status)
values ('三只松鼠', '三只松鼠股份有限公司', 5, '好吃不上火', 0),
       ('华为', '华为技术有限公司', 100, '华为致力于把数字世界带入每个人、每个家庭、每个组织，构建万物互联的智能世界', 1),
       ('小米', '小米科技有限公司', 50, 'are you ok', 1);

IDEA添加插件mybatisx
在file setting里的plugins里搜索下载即可

然后创建对应的接口和映射文件，还有实体类brand

在test下的文件里建立对应的测试文件

注意mybatis-config.xml，这是我的全局配置文件

<?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>

    <typeAliases>
        <package name="pojo"/>
    </typeAliases>

    <!--
    environments：配置数据库连接环境信息。可以配置多个environment，通过default属性切换不同的environment
    -->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!--数据库连接信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///mybatis?useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="111111"/>
            </dataSource>
        </environment>

        <environment id="test">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!--数据库连接信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///mybatis?useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="111111"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
       <!-- 加载sql映射文件
        <mapper resource="mapper/UserMapper.xml"/>
        <mapper resource="mapper/BrandMapper.xml"/>-->

        <!--Mapper代理方式-->
        <package name="mapper"/>
    </mappers>
</configuration>

这种方法可以加载你该包下所有的映射文件，就不要一个个文件添加。

你的包含实体类的文件夹

brand.java

package pojo;

public class brand {

        // id 主键
        private Integer id;
        // 品牌名称
        private String brandName;
        // 企业名称
        private String companyName;
        // 排序字段
        private Integer ordered;
        // 描述信息
        private String description;
        // 状态：0：禁用  1：启用
        private Integer status;

    public Integer getId() {
        return id;
    }

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

    public String getBrandName() {
        return brandName;
    }

    public void setBrandName(String brandName) {
        this.brandName = brandName;
    }

    public String getCompanyName() {
        return companyName;
    }

    public void setCompanyName(String companyName) {
        this.companyName = companyName;
    }

    public Integer getOrdered() {
        return ordered;
    }

    public void setOrdered(Integer ordered) {
        this.ordered = ordered;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public Integer getStatus() {
        return status;
    }

    public void setStatus(Integer status) {
        this.status = status;
    }

    @Override
    public String toString() {
        return "brand{" +
                "id=" + id +
                ", brandName='" + brandName + '\'' +
                ", companyName='" + companyName + '\'' +
                ", ordered=" + ordered +
                ", description='" + description + '\'' +
                ", status=" + status +
                '}';
    }
}

BrandMapper.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">
<!--
    namespace:名称空间,必须是对应接口的全限定名
-->
<mapper namespace="mapper.BrandMapper">

    <!--
    数据库的姓名是brand_name,实体类的姓名是brandName。即数据库表的字段名称和实体类属性名称不一样，
    则不能自动封装，需要手动封装。
    * 起别名，但是每次查询都要起一次
    * resultMap
    -->
    <resultMap id="brandResultMap" type="brand">
        <!--
                id：完成主键字段的映射
                    column：表的列名
                    property：实体类的属性名
                result：完成一般字段的映射
                    column：表的列名
                    property：实体类的属性名
            -->
        <result column="brand_name" property="brandName"/>
        <result column="company_name" property="companyName"/>
    </resultMap>

    <select id="selectAll" resultMap="brandResultMap">
       select * from tb_brand;
    </select>
    <!--<select id="selectAll" resultType="pojo.brand">
        select *
        from tb_brand;
    </select>-->
</mapper>

BrandMapper.java

```bash
package mapper;
import pojo.brand;
import java.util.List;

public interface BrandMapper {

   //查询所有
   List<brand> selectAll();
}

myBatisTest,java

package demoTest;

import mapper.BrandMapper;
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.Test;
import pojo.brand;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class myBatisTest {

    @Test
    public void testSelectAll() throws IOException {
        //1. 获取SqlSessionFactory
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        //2. 获取SqlSession对象
        SqlSession sqlSession = sqlSessionFactory.openSession();

        //3. 获取Mapper接口的代理对象
        BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);

        //4. 执行方法
        List<brand> brands = brandMapper.selectAll();
        System.out.println(brands);

        //5. 释放资源
        sqlSession.close();

    }
}

点击运行可以实现所有数据查询。

根据id进行查询

BrandMapper.java

//根据id进行查询
   List<brand> selectById(int id);

BrandMapper.xml

 <select id="selectById" resultMap="brandResultMap">
        select * from tb_brand where id = #{id};

    </select>

其中关于那个sql语句
参数占位符：

不常用，会存在参数注入问题

使用时机：
* 参数传递的时候：#{}
* 表名或者列名不固定的情况下：${} 会存在SQL注入问题
* 参数类型：parameterType：可以省略
* 特殊字符处理：
1. 转义字符：&lt(<)
2. CDATA区:

<select id="selectById" resultMap="brandResultMap">
        select *
        from tb_brand
        where id
         <![CDATA[
               <
         ]]>
         #{id};
    </select>

myBatisTest.java

 @Test
    public void testSelectById() throws IOException {
        int id = 1;
        //1. 获取SqlSessionFactory
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        //2. 获取SqlSession对象
        SqlSession sqlSession = sqlSessionFactory.openSession();

        //3. 获取Mapper接口的代理对象
        BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);

        //4. 执行方法
        List<brand> brands = brandMapper.selectById(id);
        System.out.println(brands);

        //5. 释放资源
        sqlSession.close();

    }

条件查询

多条件满足查询

1、接口方法参数使用 @Param 方式调用的方法

BrandMapper.java

  List<brand> selectByCondition(@Param("status") int status,
 @Param("companyName") String companyName, @Param("brandName") String
brandName);

BrandMapper.xml

 <!--条件查询-->
    <select id="selectByCondition" resultMap="brandResultMap">
        select *
        from tb_brand
        where status = #{status}
          and company_name like #{companyName}
          and brand_name like #{brandName}
    </select>

myBatisTest.java

 @Test
    public void testSelectCondition() throws IOException {
        //接收参数
        int status = 1;
        String companyName = "华为";
        String brandName = "华为";

        // 处理参数
        companyName = "%" + companyName + "%";
        brandName = "%" + brandName + "%";

        //1. 获取SqlSessionFactory
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        //2. 获取SqlSession对象
        SqlSession sqlSession = sqlSessionFactory.openSession();

        //3. 获取Mapper接口的代理对象
        BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);

        //4. 执行方法
        List<brand> brands = brandMapper.selectByCondition(status,companyName,brandName);
        System.out.println(brands);

        //5. 释放资源
        sqlSession.close();

    }