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
@Datapublic 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
@Datapublic class Cat implements Serializable { private static final long serialVersionUID = -39783356260765568L; private Integer id; private String name; /** * 猫的历史 */ private String history; /** * 猫的特征 */ private String features; /** * 大概的样子 */ 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_idfrom mybatis.person p left join mybatis.cat c on p.PersonId = c.person_idwhere 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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在向山靠近一点，才发现这座山，好象一位诗人遥望远方，
