spring boot 2使用Mybatis多表關聯查詢

模擬業務關系：
一個用戶user有對應的一個公司company，每個用戶有多個賬戶account。

spring boot 2的環境搭建見上文：spring boot 2整合mybatis

一、mysql創表和模擬數據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、創建實體

public class User {        
    private Integer id;
    private String name;
    private Company company;
    private List<Account> accounts;    
    //getter/setter 這里省略...
}

public class Company {
    private Integer id;
    private String companyName;
        //getter/setter 這里省略...
}

public class Account {
    private Integer id;
    private String accountName;
    //getter/setter 這里省略...

}

三、開發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 {
    /*
     * 根據用戶id查詢賬戶信息
     */
    @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 {
    /*
     * 根據公司id查詢公司信息
     */
    @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 {
    
    /*
     * 一對一查詢
     * property：查詢結果賦值給此實體屬性
     * column：對應數據庫的表字段，做為下面@One(select方法的查詢參數
     * one：一對一的查詢
     * @One(select = 方法全路徑) ：調用的方法
     */
    @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);
    
    /*
     * 一對多查詢
     * property：查詢結果賦值給此實體屬性
     * column：對應數據庫的表字段，可做為下面@One(select方法)的查詢參數
     * many：一對多的查詢
     * @Many(select = 方法全路徑) ：調用的方法
     */
    @Select("SELECT * FROM user WHERE id = #{id}")
    @Results({ 
        @Result(property = "id", column = "id"),//加此行，否則id值為空
        @Result(property = "accounts", column = "id", many = @Many(select = "com.example.demo.mapper.AccountMapper.getAccountByUserId"))
    })
    User getUserWithAccount(Long id);
    
    /*
     * 同時用一對一、一對多查詢
     */
    @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

參考上文spring boot 2整合mybatis配置application.properties和mybatis-config.xml等后，
以上面的getAll()方法為例，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" />    
        <!--封裝映射company表數據，user表與company表1對1關系，配置1對1的映射
            association:用於配置1對1的映射
                        屬性property：company對象在user對象中的屬性名
                        屬性javaType：company屬性的java對象 類型
                        屬性column：user表中的外鍵引用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對多關系映射
            property：在user里面的List<Account>的屬性名            
            ofType:當前account表的java類型
            column:外鍵
        -->
        <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、控制層

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;
    
    //請求例子：http://localhost:9001/getUserWithCompany/1
    /*請求結果：{"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;
    }
    

    //請求例子：http://localhost:9001/getUserWithAccount/1
    /*請求結果：{"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;
    }
    

    //請求例子：http://localhost:9001/getUserWithAccount/1
    /*請求結果：[{"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;
    }    
}