Spring boot2基于Mybatis实现多表关联查询

模拟业务关系：

一个用户user有对应的一个公司company，每个用户有多个账户account。

spring boot 2的环境搭建见上文：spring boot 2整合mybatis

一、mysql创表和模拟数据sql

create table if not exists `user` (
 `id` int(11) not null auto_increment,
 `name` varchar(50) not null,
 `company_id` int(11) not null,
 primary key (`id`)
) engine=innodb default charset=utf8;

create table if not exists `company` (
 `id` int(11) not null auto_increment,
 `name` varchar(200) not null,
  primary key (`id`)
) engine=innodb default charset=utf8;

create table if not exists `account` (
 `id` int(11) not null auto_increment, 
 `name` varchar(200) not null,
 `user_id` int(11) not null, 
 primary key (`id`)
) engine=innodb default charset=utf8;


insert into
  `user`
values
  (1, 'aa', 1),
  (2, 'bb', 2);

insert into
  `company`
values
  (1, 'xx公司'),
  (2, 'yy公司');

insert into
  `account`
values
  (1, '中行', 1),
  (2, '工行', 1),
  (3, '中行', 2);

二、创建实体

public class user {    
  private integer id;
  private string name;
  private company company;
  private list<account> accounts;  
  //getter/setter 这里省略...
}

public class company {
  private integer id;
  private string companyname;
    //getter/setter 这里省略...
}

public class account {
  private integer id;
  private string accountname;
  //getter/setter 这里省略...

}

三、开发mapper

方法一：使用注解

1、accountmapper.java

package com.example.demo.mapper;

import java.util.list;

import org.apache.ibatis.annotations.result;
import org.apache.ibatis.annotations.results;
import org.apache.ibatis.annotations.select;
import com.example.demo.entity.account;
public interface accountmapper {
  /*
   * 根据用户id查询账户信息
   */
  @select("select * from `account` where user_id = #{userid}")
  @results({
    @result(property = "accountname", column = "name")
  })
  list<account> getaccountbyuserid(long userid);
}

2、companymapper.java

package com.example.demo.mapper;

import org.apache.ibatis.annotations.result;
import org.apache.ibatis.annotations.results;
import org.apache.ibatis.annotations.select;

import com.example.demo.entity.company;

public interface companymapper {
  /*
   * 根据公司id查询公司信息
   */
  @select("select * from company where id = #{id}")
  @results({
    @result(property = "companyname", column = "name")
  })
  company getcompanybyid(long id);
}

3、usermapper.java

package com.example.demo.mapper;

import org.apache.ibatis.annotations.result;
import org.apache.ibatis.annotations.results;
import org.apache.ibatis.annotations.select;
import org.apache.ibatis.annotations.one;
import org.apache.ibatis.annotations.many;

import com.example.demo.entity.user;

public interface usermapper {
  
  /*
   * 一对一查询
   * property：查询结果赋值给此实体属性
   * column：对应数据库的表字段，做为下面@one(select方法的查询参数
   * one：一对一的查询
   * @one(select = 方法全路径) ：调用的方法
   */
  @select("select * from user where id = #{id}")
  @results({
    @result(property = "company", column = "company_id", one = @one(select = "com.example.demo.mapper.companymapper.getcompanybyid"))    
  })
  user getuserwithcompany(long id);
  
  /*
   * 一对多查询
   * property：查询结果赋值给此实体属性
   * column：对应数据库的表字段，可做为下面@one(select方法)的查询参数
   * many：一对多的查询
   * @many(select = 方法全路径) ：调用的方法
   */
  @select("select * from user where id = #{id}")
  @results({ 
    @result(property = "id", column = "id"),//加此行，否则id值为空
    @result(property = "accounts", column = "id", many = @many(select = "com.example.demo.mapper.accountmapper.getaccountbyuserid"))
  })
  user getuserwithaccount(long id);
  
  /*
   * 同时用一对一、一对多查询
   */
  @select("select * from user")
  @results({
    @result(property = "id", column = "id"),
    @result(property = "company", column = "company_id", one = @one(select = "com.example.demo.mapper.companymapper.getcompanybyid")),
    @result(property = "accounts", column = "id", many = @many(select = "com.example.demo.mapper.accountmapper.getaccountbyuserid"))
  })
  list<user> getall();  
}

方法二：使用xml

参考上文spring boot 2整合mybatis配置application.properties和mybatis-config.xml等后，
以上面的getall()方法为例，usermapper.xml配置如下：

<?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.example.demo.mapper.usermapper" >
  <resultmap id="usermap" type="com.example.demo.entity.user">
    <id column="id" jdbctype="integer" property="id" />
    <result property="name" column="name" jdbctype="varchar" />  
    <!--封装映射company表数据，user表与company表1对1关系，配置1对1的映射
      association:用于配置1对1的映射
            属性property：company对象在user对象中的属性名
            属性javatype：company属性的java对象 类型
            属性column：user表中的外键引用company表
    -->
    <association property="company" javatype="com.example.demo.entity.company" column="company_id">
      <id property="id" column="companyid"></id>
      <result property="companyname" column="companyname"></result>      
    </association>
    <!--配置1对多关系映射
      property：在user里面的list<account>的属性名      
      oftype:当前account表的java类型
      column:外键
    -->
    <collection property="accounts" oftype="com.example.demo.entity.account" column="user_id">
      <id property="id" column="accountid"></id>
      <result property="accountname" column="accountname"></result>      
    </collection>    
   </resultmap>

  <select id="getall" resultmap="usermap" >
    select 
    u.id,u.name,c.id companyid, c.name companyname, a.id accountid,a.name accountname 
    from user u 
    left join company c on u.company_id=c.id
    left join account a on u.id=a.user_id
  </select>
</mapper>

四、控制层

package com.example.demo.web;

import org.springframework.beans.factory.annotation.autowired;
import org.springframework.web.bind.annotation.pathvariable;
import org.springframework.web.bind.annotation.requestmapping;
import org.springframework.web.bind.annotation.restcontroller;

import com.example.demo.entity.user;
import com.example.demo.mapper.usermapper;

@restcontroller
public class usercontroller {
  @autowired
  private usermapper usermapper;
  
  //请求例子：http://localhost:9001/getuserwithcompany/1
  /*请求结果：{"id":1,"name":"aa","company":{"id":1,"companyname":"xx公司"},"accounts":null}*/
  @requestmapping("/getuserwithcompany/{id}")
  public user getuserwithcompany(@pathvariable("id") long id) {
    user user = usermapper.getuserwithcompany(id);
    return user;
  }
  

  //请求例子：http://localhost:9001/getuserwithaccount/1
  /*请求结果：{"id":1,"name":"aa","company":null,"accounts":[{"id":1,"accountname":"中行"},{"id":2,"accountname":"工行"}]}*/
  @requestmapping("/getuserwithaccount/{id}")
  public user getuserwithaccount(@pathvariable("id") long id) {
    user user = usermapper.getuserwithaccount(id);
    return user;
  }
  

  //请求例子：http://localhost:9001/getuserwithaccount/1
  /*请求结果：[{"id":1,"name":"aa","company":{"id":1,"companyname":"xx公司"},"accounts":[{"id":1,"accountname":"中行"},
    {"id":2,"accountname":"工行"}]},{"id":2,"name":"bb","company":{"id":2,"companyname":"yy公司"},"accounts":[{"id":3,"accountname":"中行"}]}]*/
  @requestmapping("/getusers")
  public list<user> getusers() {
    list<user> users=usermapper.getall();
    return users;
  }  
}

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