简单使用

Mapper动态代理开发遵从的规范

• sql映射文件的namespace必须和mapper接口的全限定类名保持一致
• mapper接口的接口方法名必须和xml中的sql语句id保持一致
• mapper接口的接口方法形参类型必须和sql语句的输入参数类型保持一致
• mapper接口的接口方法返回类型必须和sql语句的resultType保持一致

1. 定义接口(放到mapper包下,将mapper的xml放到和接口同样的路径）

   public interface UserMapper {
       User queryUserById(Integer id);
   }
   

2. 配置mapper.xml文件

   <!-- namespace属性值=接口全限定名-->
   <mapper namespace="com.itheima.mapper.UserMapper">
      <!-- id属性值=方法名-->
      <select id="queryUserById" parameterType="Integer" resultType="com.itheima.pojo.User">
         select * from user where id=#{id}
     </select>
   </mapper>
   

   
3. 使用

   @Test
   public void userMapper() throws IOException {
       InputStream inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
       SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
       SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);
       SqlSession sqlSession = sqlSessionFactory.openSession();
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       User user = mapper.queryUserById(2);
       System.out.println(user);
   }
   

全局配置文件mappers

• mappers注册sql映射文件的
  • resource属性加载sql映射文件
  • mapper class 单个注册
  • package 批量扫描注册

<mappers>
    <mapper resource="mapper/UserMapper.xml" />
    <mapper class="com.itheima.mapper.UserMapper"></mapper>
    <package name="com.itheima.mapper"></package>
</mappers>

使用注解简化（去掉mappper.xml）

传统xml的配置方式

public interface UserMapper {
	int saveUser(User user);
    List<User> queryUser();
}

<?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">
<!--属性值，必须和接口全名一致-->
<mapper namespace="com.itheima.mapper.UserMapper">

    <insert id="saveUser" parameterType="user">
          insert into user values (null,#{username},#{sex},#{birthday},#{address})
    </insert>
    
    <select id="queryUser" resultType="user">
        select * from user
    </select>
    
</mapper>

通过注解去简化可以变成

public interface UserMapper {
	@Insert(" insert into user values (null,#{username},#{sex},#{birthday},#{address})")
    int saveUser(User user);

	@Select("select * from user")
    List<User> queryUser();
}