标签：sele 分步查询 mapper 类型 字段 利用 bsp ast public
实体关系图，一个国家对应多个城市
一对多关联查询可用三种方式实现：
利用collection标签实现一对多单步关联查询：
实体类
public class CountryPlus { Long id; String name; Date lastUpdate; List<City> cityList; }
public class City { Long id; String name; Long countryId; Date lastUpdate; }
查询标签
<select id="selectCountryPlusById" resultMap="countryPlusResultMap"> select country.country_id as country_id, country, country.last_update as last_update, city_id, city, city.country_id as city_country_id, city.last_update as city_last_update from country left join city on country.country_id = city.country_id where country.country_id=#{id} </select>
resultMap
<resultMap id="countryPlusResultMap" type="canger.study.chapter04.bean.CountryPlus"> <id column="country_id" property="id"/> <result column="country" property="name"/> <result column="last_update" property="lastUpdate"/> <collection property="cityList" ofType="canger.study.chapter04.bean.City"> <id column="city_id" property="id"/> <result column="city" property="name"/> <result column="city_country_id" property="countryId"/> <result column="city_last_update" property="lastUpdate"/> </collection> </resultMap>
利用collection标签进行分步查询
select标签
<select id="selectCountryPlusByIdStep" resultMap="countryPlusResultMapStep"> select * from country where country_id=#{id} </select>
resultMap标签
<resultMap id="countryPlusResultMapStep" type="canger.study.chapter04.bean.CountryPlus"> <id column="country_id" property="id"/> <result column="country" property="name"/> <result column="last_update" property="lastUpdate"/> <collection property="cityList" select="canger.study.chapter04.mapper.CityMapper.selectCityByCountryId" column="country_id"> </collection> </resultMap>
利用association标签进行分步查询
和使用collection标签的方式相同
标签：sele 分步查询 mapper 类型 字段 利用 bsp ast public
原文地址：https://www.cnblogs.com/canger/p/9997422.html
