Mybatis Plus

1. public interface UserMapper extends BaseMapper<User> {}
   

   public class MapperTest {
    
       @Autowired
       private UserMapper userMapper;
    
       @Test
       public void getAll() {
           List<User> users = userMapper.selectList(null);
           users.forEach(System.out::println);
       }
   }
   

   只是用到了usermapper中的selectList()方法，而UserMapper继承了BaseMapper这个接口，这个接口便是MybatisPlus提供给我们的

2. 条件构造器wrapper

       @Test
       public void test01(){
           QueryWrapper<User> wrapper = new QueryWrapper<>();
           //查询名字和邮箱都不为空、且年龄大于18岁的用户
           wrapper.isNotNull("name")
                   .isNotNull("email")
                   .ge("age",18);
   
           userMapper.selectList(wrapper).forEach(System.out::println);
       }
   

3. xml映射文件

   <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
   <mapper namespace="com.xxx.mapper.UserMapper">
       <select id="selectAdultUsers" resultType="com.xxx.entity.User">
           SELECT * FROM users 
           <where>
               <if test="status != null">
                   status = #{status}
               </if>
               age >= 18
           </where>
       </select>
       
       <resultMap id="userDetailMap" type="com.xxx.entity.User">
           <id property="id" column="user_id"/>
           <result property="createTime" column="create_time"/>
       </resultMap>
       
       <select id="selectUserDetail" resultMap="userDetailMap">
           SELECT u.id AS user_id, u.create_time FROM users u
           LEFT JOIN dept d ON u.dept_id = d.id
       </select>
   </mapper>
   

   List<User> selectAdultUsers(@Param("status") String status);
   List<User> selectUserDetail();