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]]