在项目中,使用mybatis做一对多关联,出现数据条数不匹配的情况,比如要查询10条,由于一对多的关系导致最终得到的数据条数变少。
外键abum_id关联tp_abum表的主键,表结构如下:
实体:
xml:
保存后的数据如下:
sql:SELECT
abum.*,summary.id AS summary_id,
summary.summary,
summary.type AS summary_type,
summary.compositor
from
`tp_abum` abum
left join
`tp_abum_summary` summary
on
abum.id = summary.abum_id
where `status` <> '0' and create_member_code ='1' ORDER BY create_time desc limit 0,10;
获得数据:
很明显,mybatis一对多处理后,TPAbumAO的记录数少于10条。
原因是tp_abum和tp_abum_summary关联查询时,由于重复数据导致分页取到tp_abum表的数据不完整,解决方法是外面不用limit,在where条件中,对abum_id使用in子查询,在in子查询里面用limit,取出指定limit的满足条件还没有外连接的评论的id.
sql:SELECT
abum.*,
summary.id AS summary_id,
summary.summary,
summary.type AS summary_type,
summary.compositor
from
`tp_abum` abum
left join
`tp_abum_summary` summary
on
abum.id = summary.abum_id
where abum.id in (SELECT TEMP.id from (SELECT id from `tp_abum` where `status` <> '0' and create_member_code ='1' ORDER BY create_time desc limit 0,10) as temp) ORDER BY abum.create_time desc ;
最后查询结果即是正确的分页结果:
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<!--分页查询 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX --> <select id="selectCompanyAmbientInfo" resultMap="companyAndAmbient"> select a.*,b.province,b.city,b.county,c.* from t_company a left join t_company_address b on a.count_id = b.aid left join php_ambient c on a.name = c.psname and c.updatetime = (select max(updatetime) from php_ambient) where a.id in (select x.id from t_company x left join php_ambient y on x.name=y.psname and y.updatetime = (select max(z.updatetime) from php_ambient z) <where> x.delete is null <if test="info.en_name!=null and info.en_name!=''">and x.name like CONCAT('%',#{info.en_name},'%' )</if> <if test="info.countId!=null and info.countId!=''">and x.count_id = #{info.countId}</if> <if test="info.followLevel!=null and info.followLevel!=''">and x.follow_level = #{info.followLevel}</if> <if test="info.isonlineMonitor!=null and info.isonlineMonitor!=''">and x.isonline_monitor = #{info.isonlineMonitor}</if> <if test="info.trade!=null and info.trade!=''">and x.trade = #{info.trade}</if> <if test="code=='so2,nox,pm'"> and y.isso2 = 1 and y.isnox = 1 and c.ispm = 1 </if> <if test="code=='so2,nox'"> and y.isso2 = 1 and y.isnox = 1 </if> <if test="code=='nox,pm'"> and y.isnox = 1 and y.ispm = 1 </if> <if test="code=='so2'"> and y.isso2 = 1 </if> <if test="code=='nox'"> and y.isnox = 1 </if> <if test="code=='pm'"> and y.ispm = 1 </if> </where> GROUP BY(x.id) ORDER BY x.isonline_monitor desc limit #{pageSize} offset #{pageNum}) </select>