Spring boot2基于Mybatis实现多表关联查询
更新时间:2020年04月23日 09:59:56 作者:gdjlc
这篇文章主要介绍了Spring boot2基于Mybatis实现多表关联查询,文中通过示例代码介绍的非常详细,对大家的学习或者工作具有一定的参考学习价值,需要的朋友可以参考下
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; } }
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持脚本之家。
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