mybatis的＜foreach＞标签使用

柔光的暖阳◎ 2024-04-23 03:21 7阅读 0赞

**记录**：419

**场景**：使用MyBatis的<foreach></foreach>标签的循环遍历List类型的入参。使用collection属性指定List，item指定List中存放的对象，separator指定分割符号，open指定开始字符，close指定结束字符。

**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(...)+>，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****<****foreach****></****foreach****>标签元素**

**场景**：<foreach></foreach>标签元素在<insert><update><delete><select>等标签元素内使用。

**示例功能**：示例使用<foreach></foreach>标签，在<insert><update><delete><select>标签内遍历输入的List类型入参。

**2.1Java接口**

@Repository
    public interface Label03ForeachMapper {
      List<CityLabelPO> queryCity(List<Long> paraList);
      int insertCity(List<CityLabelPO> cityList);
      int insertCityUnionAll(List<CityLabelPO> cityList);
      int updateCity(List<CityLabelPO> cityList);
      int deleteCity(List<CityLabelPO> cityList);
    }

**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.Label03ForeachMapper">
      
      <select id="queryCity" resultType="com.hub.example.domain.CityLabelPO">
          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
          WHERE CITY_ID IN
          <foreach collection="list" item="cityId" open="(" separator="," close=")">
              #{cityId}
          </foreach>
      </select>
      
      <insert id="insertCity" parameterType="java.util.List">
          insert into t_city_01 (CITY_ID,
          CITY_NAME,
          LAND_AREA,
          POPULATION,
          GROSS,
          CITY_DESCRIBE,
          DATA_YEAR,
          UPDATE_TIME)
          values
          <foreach collection="list" item="cityPO" open="" separator="," close="">
              (#{cityPO.cityId},
              #{cityPO.cityName},
              #{cityPO.landArea},
              #{cityPO.population},
              #{cityPO.gross},
              #{cityPO.cityDescribe},
              #{cityPO.dataYear},
              #{cityPO.updateTime})
          </foreach>
      </insert>
      
      <insert id="insertCityUnionAll" parameterType="java.util.List">
          insert into t_city_01 (CITY_ID,
          CITY_NAME,
          LAND_AREA,
          POPULATION,
          GROSS,
          CITY_DESCRIBE,
          DATA_YEAR,
          UPDATE_TIME)
          <foreach collection="list" item="cityPO" open="" separator="UNION ALL" close="">
              select
              #{cityPO.cityId},
              #{cityPO.cityName},
              #{cityPO.landArea},
              #{cityPO.population},
              #{cityPO.gross},
              #{cityPO.cityDescribe},
              #{cityPO.dataYear},
              #{cityPO.updateTime}
              from dual
          </foreach>
      </insert>
      
      <update id="updateCity" parameterType="java.util.List">
          update
          t_city_01
          set CITY_DESCRIBE='杭州是一个发达城市'
          WHERE CITY_ID IN
          <foreach collection="list" item="cityPO" open="(" separator="," close=")">
              #{cityPO.cityId}
          </foreach>
      </update>
      
      <delete id="deleteCity" parameterType="java.util.List">
          delete from t_city_01 where 1=1
          <if test="list.size()>0">
              AND CITY_ID IN
              <foreach collection="list" item="cityPO" open="(" separator="," close=")">
                  #{cityPO.cityId}
              </foreach>
          </if>
      </delete>
    </mapper>

**3.测试**

**3.1测试代码**

@Slf4j
    @RestController
    @RequestMapping("/hub/example/cityLabel")
    public class CityLabelController {
      @Autowired
      private Label03ForeachMapper label03ForeachMapper;
      @GetMapping("/load03")
      public Object load03() {
        log.info("测试开始...");
        // 生成查询参数
        List<Long> paraList = Arrays.asList(1L, 2L, 3L);
        // 1.查询时,使用<foreach></foreach>标签
        List<CityLabelPO> list01 = label03ForeachMapper.queryCity(paraList);
        // 2.1插入时,使用<foreach></foreach>标签,使用逗号分割
        label03ForeachMapper.insertCity(list01);
        // 2.2插入时,使用<foreach></foreach>标签,使用union all分割
        paraList = Arrays.asList(4L, 5L, 6L);
        List<CityLabelPO> list02 = label03ForeachMapper.queryCity(paraList);
        label03ForeachMapper.insertCityUnionAll(list02);
        // 3.更新时,使用<foreach></foreach>标签
        label03ForeachMapper.updateCity(list01);
        // 4.删除时,使用<foreach></foreach>标签
        label03ForeachMapper.deleteCity(list01);
        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/load03

**3.3执行SQL**

示例使用<foreach></foreach>标签后，遍历List类型入参，从具体对象中取值。

示例一，查询时,使用<foreach></foreach>标签。

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
    WHERE CITY_ID IN (?, ?, ?)

示例二,插入时,使用<foreach></foreach>标签,使用逗号分割。

INSERT INTO t_city_01 (
      CITY_ID,
      CITY_NAME,
      LAND_AREA,
      POPULATION,
      GROSS,
      CITY_DESCRIBE,
      DATA_YEAR,
      UPDATE_TIME
    )
    VALUES
      (?, ?, ?, ?, ?, ?, ?, ?),
      (?, ?, ?, ?, ?, ?, ?, ?),
      (?, ?, ?, ?, ?, ?, ?, ?)

示例三,插入时,使用<foreach></foreach>标签,使用union all分割。

INSERT INTO t_city_01 (CITY_ID, CITY_NAME, LAND_AREA, 
     POPULATION, GROSS, CITY_DESCRIBE, DATA_YEAR, UPDATE_TIME) 
    SELECT ?, ?, ?, ?, ?, ?, ?, ? FROM DUAL 
    UNION ALL 
    SELECT ?, ?, ?, ?, ?, ?, ?, ? FROM DUAL 
    UNION ALL 
    SELECT ?, ?, ?, ?, ?, ?, ?, ? FROM DUAL

示例四,更新时,使用<foreach></foreach>标签。

UPDATE
      t_city_01
    SET
      CITY_DESCRIBE = '杭州是一个发达城市'
    WHERE CITY_ID IN (?, ?, ?)

示例五,删除时,使用<foreach></foreach>标签。

DELETE
    FROM
      t_city_01
    WHERE 1 = 1
      AND CITY_ID IN (?, ?, ?)

**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;
    }

**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