spring boot 2使用Mybatis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;

    }

}

巴特西

spring boot 2使用Mybatis多表关联查询

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