今天同学突然问我这个怎么搞。
然后自己搞了一下发现这个玩意有坑。。就记录一下
0. 表结构
person表
cat表
一个person有多个cat
实体类就这么写
1. 实体类
Person实体类
@Data
public class Person implements Serializable {
private static final long serialVersionUID = -70682701290685641L;
private Integer personid;
private String firstname;
private String lastname;
private List<Cat> cats;
}Cat实体类
@Data
public class Cat implements Serializable {
private static final long serialVersionUID = -39783356260765568L;
private Integer id;
private String name;
private String history;
private String features;
private String imgurl;
private Integer personId;
}2. Mapper配置文件
PersonDao.xml
<?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.liliya.dao.PersonDao">
<!-- 返回的Person映射Map -->
<resultMap type="com.liliya.entity.Person" id="PersonMap">
<result property="personid" column="PersonId" jdbcType="INTEGER"/>
<result property="firstname" column="FirstName" jdbcType="VARCHAR"/>
<result property="lastname" column="LastName" jdbcType="VARCHAR"/>
<collection property="cats" ofType="Cat">
<result property="id" column="id" jdbcType="INTEGER"/>
<result property="name" column="name" jdbcType="VARCHAR"/>
<result property="history" column="history" jdbcType="VARCHAR"/>
<result property="features" column="features" jdbcType="VARCHAR"/>
<result property="imgurl" column="imgUrl" jdbcType="VARCHAR"/>
<result property="personId" column="person_id" jdbcType="INTEGER"/>
</collection>
</resultMap>
<!--查询单个-->
<select id="queryById" resultMap="PersonMap">
select personid, firstname, lastname, id, name, history, features, imgurl, person_id
from mybatis.person p inner join mybatis.cat c on p.PersonId = c.person_id
and PersonId= #{PersonId}
</select>
</mapper>上面这个是查询单个人的，但是分页没有这么简单
一开始我以为是这么写的,就简单的加一个limit
<select id="queryById" resultMap="PersonMap">
select personid, firstname, lastname, id, name, history, features, imgurl, person_id
from mybatis.person p inner join mybatis.cat c on p.PersonId = c.person_id
limit #{page},#{step}
</select>然后查出来就是这个吊样。。。很明显嘛，不对我的胃口。。
后面我准备放弃的时候突然想到可以来一个子查询。。。
然后我就写出了这样的sql
,在子查询里面套子查询。。。实现limit分页的效果
select personid, firstname, lastname, id, name, history, features, imgurl, person_id
from mybatis.person p left join mybatis.cat c on p.PersonId = c.person_id
where PersonId in (select pp.PersonId from (select person.PersonId from person limit 2,2) as pp);然后sql放到上面就搞好了
跑出来的效果就非常nice
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