Mybatis--查询collection--List<String>

描述下场景，比如一个人有多个qq号（假设一个人可以有重复的qq号）

数据库结构，有两张表：
people表
id	name
1	jack

people_qq表
id	people_id	qq
1	1	123456
2	1	234567
3	1	456789
4	1	123456

实体类：

import java.io.Serializable;
import java.util.List;

public class People implements Serializable{

private static final long serialVersionUID = -5935066186174346694L;
private Long id;
private String name;
private List<String> qqs;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<String> getQqs() {
return qqs;
}
public void setQqs(List<String> qqs) {
this.qqs = qqs;
}
@Override
public String toString() {
return "People [id=" + id + ", name=" + name + ", qqs=" + qqs + "]";
}
}

mapper接口：

import com.hnpicheng.mybatisissue.domain.People;

public interface PeopleMapper {
People selectPeopleById( Long id);
}

测试代码：

import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.hnpicheng.mybatisissue.domain.People;
import com.hnpicheng.mybatisissue.mapper.PeopleMapper;

public class App
{
public static void main( String[] args )
{
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring-mybatis.xml");
PeopleMapper peopleMapper = context.getBean(PeopleMapper.class);
People p = peopleMapper.selectPeopleById(1L);
System.out.println(p);

}
}

PeopleMapper.xml

根据业务需要，如果不需要将重复数据查出来：
那么可以使用

<?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.hnpicheng.mybatisissue.mapper.PeopleMapper">

<resultMap id="peopleResultMap" type="People">
<id property="id" column="id" />
<result property="name" column="name" />
<collection property="qqs" ofType="string" javaType="list">
<result column="qq" />
</collection>
</resultMap>

<select id="selectPeopleById" resultMap="peopleResultMap">
select p.*,pq.qq from
people p left join  people_qq pq on p.id = pq.people_id
where p.id = #{id}
</select>
</mapper>

测试结果，优点只要查一次，对于需要排重的查询业务，可以用这个方法：

DEBUG [main] - ==>  Preparing: select p.*,pq.qq from people p left join people_qq pq on p.id = pq.people_id where p.id = ?
DEBUG [main] - ==> Parameters: 1(Long)
DEBUG [main] - <==      Total: 4
People [id=1, name=jack, qqs=[123456, 234567, 456789]]

若果需要将重复数据查询出来，那么可以使用以下配置

<?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.hnpicheng.mybatisissue.mapper.PeopleMapper">
<resultMap id="peopleResultMap" type="People">
<id property="id" column="id" />
<result property="name" column="name" />
<collection property="qqs" column="id" select="selectQQByPeopleId">  这里的column是指调用selectQQByPeopleId传递的参数
<result column="qq" />
</collection>
</resultMap>

<select id="selectPeopleById" resultMap="peopleResultMap">
select * from people where id = #{id}
</select>

<select id="selectQQByPeopleId" resultType="string">
select qq from people_qq where people_id = #{id}
</select>
</mapper>

测试结果：

DEBUG [main] - ==>  Preparing: select * from people where id = ?
DEBUG [main] - ==> Parameters: 1(Long)
DEBUG [main] - <==      Total: 1
DEBUG [main] - ==>  Preparing: select qq from people_qq where people_id = ?
DEBUG [main] - ==> Parameters: 1(Long)
DEBUG [main] - <==      Total: 4
People [id=1, name=jack, qqs=[123456, 234567, 456789, 123456]]