Spring boot2基于Mybatis实现多表关联查询的方法

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);

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... }

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); }

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); }

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(); }

<?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" />  <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>  <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>

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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