mybaties list 返回重复数据

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mybaties list 返回重复数据

2024-07-08 20:18| 来源: 网络整理| 查看: 265

记录下mybatis的集合查询中碰到的问题

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

idname1jack

people_qq表

idpeople_idqq11123456212345673145678941123456

实体类：

Java代码复制代码收藏代码

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 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 getQqs() { return qqs; } public void setQqs(List qqs) { this.qqs = qqs; } @Override public String toString() { return "People [id=" + id + ", name=" + name + ", qqs=" + qqs + "]"; } }

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 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 getQqs() {

return qqs;

}

public void setQqs(List qqs) {

this.qqs = qqs;

}

@Override

public String toString() {

return "People [id=" + id + ", name=" + name + ", qqs=" + qqs + "]";

}

mapper接口：

Java代码复制代码收藏代码

import com.hnpicheng.mybatisissue.domain.People; public interface PeopleMapper { People selectPeopleById( Long id); }

import com.hnpicheng.mybatisissue.domain.People;

public interface PeopleMapper {

People selectPeopleById( Long id);

}

测试代码：

Java代码复制代码收藏代码

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); } }

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代码复制代码收藏代码

select p.*,pq.qq from people p left join people_qq pq on p.id = pq.people_id where p.id = #{id}

[xml] view plain copy

select p.*,pq.qq from people p left join people_qq pq on p.id = pq.people_id where p.id = #{id}

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：

Java代码复制代码收藏代码

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] - 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] - Preparing: select * from people where id = ? DEBUG [main] - ==> Parameters: 1(Long) DEBUG [main] - Preparing: select qq from people_qq where people_id = ? DEBUG [main] - ==> Parameters: 1(Long) DEBUG [main] - Preparing: select * from people where id = ?

DEBUG [main] - ==> Parameters: 1(Long)

DEBUG [main] - Preparing: select qq from people_qq where people_id = ?

DEBUG [main] - ==> Parameters: 1(Long)

DEBUG [main] -

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