MyBatis-Plus 如何实现连表查询的示例代码

// 第一步，在 mapper.java 类中定义一个连表查询的方法 selectTsxxWsla
public interface WTsxxMapper extends SuperMapper<WTsxx> {
 List<Object> selectTsxxWsla();
}

// 第二步，在 mapper.xml 中定义 id='selectTsxxWsla' 的查询块
<mapper namespace="com.haoda.sswfw.dao.primary.mapper.WTsxxMapper">
 <select id="selectTsxxWsla" resultType="map">
 SELECT a.*,CONCAT(b.xxid,'') AS xxid,b.nr,b.xxbt,b.weixzt,b.ywlxbm,b.createtime,b.glid 
 FROM v_weix_user a,w_tsxx b 
 JOIN (
   SELECT xxid,user_name,createtime FROM w_tsxx_user
    ) c ON b.xxid = c.xxid 
 WHERE a.user_name = c.user_name AND a.openid != '' AND b.weixzt = '2' AND b.errcode IS NULL AND LOWER(b.ywlxbm) = 'wsla'
 </select>
</mapper>

// 第三步，直接写测试用例，看看能出来什么效果
@RunWith(SpringRunner.class)
@SpringBootTest
public class DbTest {
 @Autowired
 private WTsxxMapper tsxxMapper;
 
 @Test
 public void test3() {
 List<Object> selectTsxxWsla = tsxxMapper.selectTsxxWsla();
 for (Object obj : selectTsxxWsla) {
  System.out.println(obj);
 }
 }
}

// 将查询字段 自定义成 WxTsxxVo
public class WxTsxxVo {
 private String openid;
 private String unionid;
 private Long user_id;
 private String user_name;
 .....
}

// 原本 List<Object> 替换成 List<WxTsxxVo>
public interface WTsxxMapper extends SuperMapper<WTsxx> {
 List<WxTsxxVo> selectTsxxWsla();
}

// 原本 List<Object> 替换成 List<WxTsxxVo>
@Test
public void test3() {
 List<WxTsxxVo> selectTsxxWsla = tsxxMapper.selectTsxxWsla();
 for (WxTsxxVo obj : selectTsxxWsla) {
 System.out.println(obj);
 }
}

// 对应 WxTsxxVo 实体类，写了一个对应的 resultMap
<resultMap id="WxTsxxVo" type="com.haoda.sswfw.job.vo.WxTsxxVo">
   <result column="openid" property="openid" />
   <result column="unionid" property="unionid" />
   <result column="user_id" property="user_id" />
   <result column="user_name" property="user_name" />
   ...
</resultMap > 

// 原先的 resultType="map" 替换成 resultMap="WxTsxxVo"
<select id="selectTsxxWsla" resultMap="WxTsxxVo">
 SELECT a.*,CONCAT(b.xxid,'') AS xxid,b.nr,b.xxbt,b.weixzt,b.ywlxbm,b.createtime,b.glid 
 FROM v_weix_user a,w_tsxx b 
 JOIN (
   SELECT xxid,user_name,createtime FROM w_tsxx_user
   ) c ON b.xxid = c.xxid 
 WHERE a.user_name = c.user_name AND a.openid != '' AND b.weixzt = '2' AND b.errcode IS NULL AND LOWER(b.ywlxbm) = 'wsla'
</select>