记录:418
场景:使用MyBatis的<choose></choose>标签的<when></when>标签的test属性,对入参属性的值做非null(!=null)、非空(!='')判断,或者与常量做相等(==)或者不等判断(!=)。
版本:JDK 1.8,Spring Boot 2.6.3,mybatis-3.5.9。
1.基础知识
1.1MyBatis的标签
(1)查看MyBatis支持的标签
地址:http://mybatis.org/dtd/mybatis-3-mapper.dtd
(2)查看标签使用
以<mapper></mapper>标签元素为例,在mybatis-3-mapper.dtd中如下:
<!ELEMENT mapper (cache-ref | cache | resultMap* | parameterMap* | sql* | insert* | update* | delete* | select* )+>
<!ATTLIST mapper
namespace CDATA #IMPLIED
>
<!ELEMENT mapper(...)+>,表示这是一个标签元素mapper.
(..| insert*| update* | delete* | select*),表示在mapper元素中可以嵌套使用的元素清单。
<!ATTLIST mapper>,表示这是一个元素标签的支持的属性。
1.2MyBatis的使用
(1)在application.yml配置文件配置mybatis映射的xml文件位置。
mybatis:
mapper-locations: classpath*:mapper/**/*.xml
(2)创建一个Java接口。在接口中添加方法。
(3)创建一个Java接口映射的xml文件。在xml中使用<mapper></mapper>标签的namespace属性指定Java接口的全路径。Java接口和xml映射文件就完成了绑定关系。
(4)在<mapper></mapper>标签内,使用<insert><update><delete><select>等标签的id属性指定Java的方法名称。Java接口的方法和xml映射文件的<mapper></mapper>内部的标签就完成了绑定关系。
2.使用<choose></choose>标签元素
场景:<choose></choose>标签元素在<insert><update><delete><select>等标签元素内使用。
一般组合:<choose><when></when><otherwise></otherwise></choose>
一般组合:<choose><when></when><when></when></choose>
示例功能:示例使用<choose></choose>标签,根据不同条件组装不同查询的SQL。
2.1Java接口
@Repository
public interface Label02ChooseMapper {
List<CityLabelPO> queryCity(CityLabelDTO cityLabelDTO);
}
2.2Java接口映射的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.hub.example.mapper.Label02ChooseMapper">
<select id="queryCity" parameterType="com.hub.example.domain.CityLabelDTO"
resultType="com.hub.example.domain.CityLabelPO">
select CITY_ID AS "cityId",
<choose>
<when test="flagColumn !=null and flagColumn !='' and flagColumn == '01' ">
CITY_NAME AS "cityName",
LAND_AREA AS "landArea",
POPULATION AS "population",
GROSS AS "gross",
CITY_DESCRIBE AS "cityDescribe",
DATA_YEAR AS "dataYear",
UPDATE_TIME AS "updateTime"
</when>
<when test="flagColumn !=null and flagColumn !='' and flagColumn == '02' ">
CITY_NAME AS "cityName",
LAND_AREA AS "landArea"
</when>
<otherwise>
CITY_NAME AS "cityName",
LAND_AREA AS "landArea",
POPULATION AS "population",
GROSS AS "gross"
</otherwise>
</choose>
from
<choose>
<when test="flagFrom !=null and flagFrom !='' and flagFrom == '01' ">
t_city
</when>
<otherwise>
t_city_01
</otherwise>
</choose>
aa
where
<choose>
<when test="cityId !=null and cityId !='' and flagWhere == '01' ">
aa.CITY_ID = #{cityId}
</when>
<when test="cityName !=null and cityName !='' and flagWhere == '02' ">
aa.CITY_NAME = #{cityName}
</when>
</choose>
</select>
</mapper>
3.测试
3.1测试代码
@Slf4j
@RestController
@RequestMapping("/hub/example/cityLabel")
public class CityLabelController {
@Autowired
private Label02ChooseMapper label02ChooseMapper;
@GetMapping("/load02")
public Object load02() {
log.info("测试开始...");
// 示例一
CityLabelDTO labelDTO = CityLabelDTO.builder()
.cityId(1L).flagColumn("01")
.flagFrom("01").flagWhere("01").build();
List<CityLabelPO> labelPOList = label02ChooseMapper.queryCity(labelDTO);
// 示例二
labelDTO = CityLabelDTO.builder()
.cityName("上海").flagColumn("02")
.flagFrom("02").flagWhere("02").build();
labelPOList = label02ChooseMapper.queryCity(labelDTO);
log.info("测试结束...");
return "执行成功";
}
}
3.2测试请求
URL:http://127.0.0.1:18080/hub-example/hub/example/cityLabel/load02
3.3执行SQL
示例使用<choose></choose>标签后,根据不同条件组装不同查询的SQL,适配不同业务场景。
示例一:
SELECT
CITY_ID AS "cityId",
CITY_NAME AS "cityName",
LAND_AREA AS "landArea",
POPULATION AS "population",
GROSS AS "gross",
CITY_DESCRIBE AS "cityDescribe",
DATA_YEAR AS "dataYear",
UPDATE_TIME AS "updateTime"
FROM
t_city aa
WHERE aa.CITY_ID = ?;
示例二:
SELECT
CITY_ID AS "cityId",
CITY_NAME AS "cityName",
LAND_AREA AS "landArea"
FROM
t_city_01 aa
WHERE aa.CITY_NAME = ?;
4.支撑
4.1实体对象
(1)封装结果对象CityLabelPO
@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class CityLabelPO {
private Long cityId;
private String cityName;
private Double landArea;
private Long population;
private Double gross;
private String cityDescribe;
private String dataYear;
private Date updateTime;
}
(2)封装参数CityLabelDTO
@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class CityLabelDTO {
private Long cityId;
private String cityName;
private Double landArea;
private Long population;
private Double gross;
private String cityDescribe;
private String dataYear;
private Date updateTime;
// 标记查询的字段
private String flagColumn;
// 标记查询的表
private String flagFrom;
// 标记where条件
private String flagWhere;
}
4.2建表语句
CREATE TABLE t_city (
CITY_ID BIGINT(16) NOT NULL COMMENT '唯一标识',
CITY_NAME VARCHAR(64) COLLATE utf8_bin NOT NULL COMMENT '城市名',
LAND_AREA DOUBLE DEFAULT NULL COMMENT '城市面积',
POPULATION BIGINT(16) DEFAULT NULL COMMENT '城市人口',
GROSS DOUBLE DEFAULT NULL COMMENT '生产总值',
CITY_DESCRIBE VARCHAR(512) COLLATE utf8_bin DEFAULT NULL COMMENT '城市描述',
DATA_YEAR VARCHAR(16) COLLATE utf8_bin DEFAULT NULL COMMENT '数据年份',
UPDATE_TIME DATETIME DEFAULT NULL COMMENT '更新时间'
) ENGINE=INNODB DEFAULT CHARSET=utf8 COLLATE=utf8_bin COMMENT='城市信息表';
以上,感谢。文章来源:https://www.toymoban.com/news/detail-714210.html
2023年4月23日文章来源地址https://www.toymoban.com/news/detail-714210.html
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