MyBatis查询所有数据

查询

1. 查询所有数据

   1. 编写接口方法：Mapper接口，参数：无，结果：List

      1. 在com.uestc.mapper创建一个BrandMapper类

         public interface BrandMapper {
         ?
             /**
              * 查询所有
              */
             public List selectAll();
         ?
         }

         2.(编写SQL语句：SQL映射文件)在resources下面的com.uestc.mapper创建一个BrandMapper.xml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">
         
         
         <mapper namespace="com.uestc.mapper.BrandMapper">
         
             
         
             
         
             <resultMap id="brandResultMap" type="brand">
                 
                 <result column="brand_name" property="brandName" />
                 <result column="company_name" property="companyName" />
         
             resultMap>
         
                 <select id="selectAll" resultMap="brandResultMap">
         
                     select
                            *
                     from tb_brand;
         
                 select>
         
             
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         mapper>

         3.(执行方法：测试)在test下面创建com.uestc.test.MyBatisTest的类

         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 brands = brandMapper.selectAll();
                 System.out.println(brands);
         ?
                 //5.释放资源
                 sqlSession.close();
             }
         }

   实体类属性名和数据库表列名不一致，不能自动封装数据

   （1）起别名：在SQL语句中，对不一样的列名起别名，别名和实体类属性名一样。*可以定义片段，提升复用性

   （2）resultMap：定义完成不一致的属性名和列名的映射。