mybatis的<choose>标签使用
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>aawhere<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 {@Autowiredprivate 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:
SELECTCITY_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"
FROMt_city aa
WHERE aa.CITY_ID = ?;
示例二:
SELECTCITY_ID AS "cityId",CITY_NAME AS "cityName",LAND_AREA AS "landArea"
FROMt_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。
2023年4月23日