MyBatis的关联查询！！！（一对一、一对多、多对多）
准备工作：
1.创建Maven工程，还没有配置Maven的和还不会的去看这里啦：maven的下载安装与配置环境变量！！！（全网最详细）-CSDN博客
Account.java : (pojo类) （这里我们说明一下，根据我们下边的需求，我们需要将两张表查询出来的数据存到Account中，所以我们在Account这个实体类中添加了一个User的属性）
package com.by.pojo;
import java.io.Serializable;
public class Account implements Serializable {
private Integer id;
private Integer uid;
private Double money;
private User user;
@Override
public String toString() {
return "Account{" +
"id=" + id +
", uid=" + uid +
", money=" + money +
", user=" + user +
'}';
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public Integer getUid() {
return uid;
}
public void setUid(Integer uid) {
this.uid = uid;
}
public Double getMoney() {
return money;
}
public void setMoney(Double money) {
this.money = money;
}
}User.java：
/*
* Copyright (c) 2020, 2023, All rights reserved.
*
*/
package com.by.pojo;
import java.io.Serializable;
import java.util.Date;
/**
* Project: mybatis - User
* Powered by scl On 2023-12-18 11:38:09
* 描述：
*
* @author 孙臣龙 [[email protected]]
* @version 1.0
* @since 17
*/
public class User implements Serializable {
private Integer id;
private String username;
private Date birthday;
private String sex;
private String address;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", birthday=" + birthday +
", sex='" + sex + '\'' +
", address='" + address + '\'' +
'}';
}
}
2.导入依赖到pom.xml文件中
org.mybatis
mybatis
3.4.5
mysql
mysql-connector-java
5.1.47
log4j
log4j
1.2.17
junit
junit
4.12
src/main/java
**/*.xml
src/main/resources
3.在resources中创建log4j.properites和mybatis-config.xml
log4j.properites:
log4j.properites:
# Global logging configuration
log4j.rootLogger=DEBUG, stdout
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%nmybatis-config.xml:
4.创建RolerMapper接口和RoleMapper.xml文件
AccountMapper.java:
package com.by.mapper;
import com.by.pojo.Account;
import java.util.List;
public interface AccountMapper {
}
AccountMapper.xml:
5.创建测试类MyBatisTest
/*
* Copyright (c) 2020, 2023, All rights reserved.
*
*/
package com.by;
import com.by.mapper.RoleMapper;
import com.by.pojo.Role;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class MyBatisTestRole {
private InputStream inputStream;
private SqlSession sqlSession;
@Before
public void init() throws IOException {
// 加载配置文件
String resource = "mybatis-config.xml";
inputStream = Resources.getResourceAsStream(resource);
// 创建sqlSessionFActory
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
// 获得数据的绘画实例
sqlSession = sessionFactory.openSession();
}
@After
public void close() throws IOException {
inputStream.close();
sqlSession.close();
}
}6.数据库文件
/*
Navicat MySQL Data Transfer
Source Server : localhost_3306
Source Server Version : 50732
Source Host : localhost:3306
Source Database : mybatis
Target Server Type : MYSQL
Target Server Version : 50732
File Encoding : 65001
Date: 2021-12-24 11:51:18
*/
SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for account
-- ----------------------------
DROP TABLE IF EXISTS `account`;
CREATE TABLE `account` (
`id` int(11) NOT NULL COMMENT '编号',
`uid` int(11) DEFAULT NULL COMMENT '用户编号',
`money` double DEFAULT NULL COMMENT '金额',
PRIMARY KEY (`id`),
KEY `FK_Reference_8` (`uid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of account
-- ----------------------------
INSERT INTO `account` VALUES ('1', '41', '1000');
INSERT INTO `account` VALUES ('2', '45', '1000');
INSERT INTO `account` VALUES ('3', '41', '2000');
-- ----------------------------
-- Table structure for role
-- ----------------------------
DROP TABLE IF EXISTS `role`;
CREATE TABLE `role` (
`ID` int(11) NOT NULL COMMENT '编号',
`ROLE_NAME` varchar(30) DEFAULT NULL COMMENT '角色名称',
`ROLE_DESC` varchar(60) DEFAULT NULL COMMENT '角色描述',
PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of role
-- ----------------------------
INSERT INTO `role` VALUES ('1', '院长', '管理整个学院');
INSERT INTO `role` VALUES ('2', '总裁', '管理整个公司');
INSERT INTO `role` VALUES ('3', '校长', '管理整个学校');
-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(32) NOT NULL COMMENT '用户名称',
`password` varchar(20) DEFAULT NULL,
`birthday` datetime DEFAULT NULL COMMENT '生日',
`sex` char(1) DEFAULT NULL COMMENT '性别',
`address` varchar(256) DEFAULT NULL COMMENT '地址',
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=49 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES ('41', '张三丰', '111', '2018-02-27 17:47:08', '男', '上海徐汇');
INSERT INTO `user` VALUES ('42', '宋远桥', '111', '2018-03-02 15:09:37', '女', '北京昌平');
INSERT INTO `user` VALUES ('43', '俞莲舟', '111', '2018-03-04 11:34:34', '女', '陕西西安');
INSERT INTO `user` VALUES ('45', '张翠山', '111', '2018-03-04 12:04:06', '男', '山东济南');
INSERT INTO `user` VALUES ('46', '殷梨亭', '111', '2018-03-07 17:37:26', '男', '河北张家口');
INSERT INTO `user` VALUES ('48', '莫声谷', '111', '2018-03-08 11:44:00', '女', '山西太原');
-- ----------------------------
-- Table structure for user_role
-- ----------------------------
DROP TABLE IF EXISTS `user_role`;
CREATE TABLE `user_role` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`uid` int(11) DEFAULT NULL,
`rid` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of user_role
-- ----------------------------
INSERT INTO `user_role` VALUES ('1', '45', '1');
INSERT INTO `user_role` VALUES ('2', '41', '1');
INSERT INTO `user_role` VALUES ('3', '45', '2');
准备工作完成后，开始功能的开发：
1.一对一的关联查询
需求：现在有两张表，根据account表中的uid和user表中的id，将这两张表结合起来查询，并返回数据。
根据需求我们，开始开发：
（1）AccountMapper.java中添加一个方法：
Account findAll(Integer id);
（2）在AccountMapper.xml文件中映射相应的方法：
（3）测试类：添加这个方法
@Test
public void findAccountById(){
AccountMapper accountMapper = sqlSession.getMapper(AccountMapper.class);
Account account = accountMapper.findAll(2);
System.out.println(account);
}
（4）结果展示：
2.一对多关联查询（一个用户可以有多个账户）
（1）首先应该在User Mapper.java文件中添加一个方法。
package com.by.mapper;
import com.by.pojo.User;
import java.util.List;
/**
* Project: mybatis - UserMapper
* Powered by scl On 2023-12-22 15:52:05
* 描述：
*
* @author 孙臣龙 [[email protected]]
* @version 1.0
* @since 17
*/
public interface UserMapper {
/**
* 一对多
*/
List findAllUserAccount(Integer id);
}
（2）在UserMapper.xml文件在实现这个方法。
（3）在User实体类中添加List
private List accountList;
public List getAccountList() {
return accountList;
}
public void setAccountList(List accountList) {
this.accountList = accountList;
} （4）编写测试类：
/*
* Copyright (c) 2020, 2023, All rights reserved.
*
*/
package com.by;
import com.by.mapper.AccountMapper;
import com.by.mapper.RoleMapper;
import com.by.mapper.UserMapper;
import com.by.pojo.Role;
import com.by.pojo.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
/**
* Project: mybatis - MyBatisTest
* Powered by scl On 2023-12-18 11:44:53
* 描述：
*
* @author 孙臣龙 [[email protected]]
* @version 1.0
* @since 17
*/
public class MyBatisTestRole {
private InputStream inputStream;
private SqlSession sqlSession;
@Before
public void init() throws IOException {
// 加载配置文件
String resource = "mybatis-config.xml";
inputStream = Resources.getResourceAsStream(resource);
// 创建sqlSessionFActory
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
// 获得数据的绘画实例
sqlSession = sessionFactory.openSession();
}
/**
* 一对多,查询一个用户名下有几张卡
*/
@Test
public void findAllUserAccount() {
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
List allUserAccount = userMapper.findAllUserAccount(41);
for (User user : allUserAccount) {
System.out.println(user);
}
}
@After
public void close() throws IOException {
inputStream.close();
sqlSession.close();
}
}
（5）结果展示：
3.多对多关联查询（查询角色及角色赋予的用户信息 ）
（1）RoleMapper接口中定义一个方法：
package com.by.mapper;
import com.by.pojo.Role;
import com.by.pojo.User;
import java.util.List;
/**
* Project: mybatis - RoleMapper
* Powered by scl On 2023-12-20 14:37:16
* 描述：
*
* @author 孙臣龙 [[email protected]]
* @version 1.0
* @since 17
*/
public interface RoleMapper {
List findAllRoleByUser(Integer id);
}
（2）在RoleMapper.xml文件中实现这个方法。
（3）实体类Role:
/*
* Copyright (c) 2020, 2023, All rights reserved.
*
*/
package com.by.pojo;
import java.util.List;
/**
* Project: mybatis - Role
* Powered by scl On 2023-12-20 14:36:04
* 描述：
*
* @author 孙臣龙 [[email protected]]
* @version 1.0
* @since 17
*/
public class Role {
private int id;
private String roleName;
private String roleDesc;
private List userList;
public List getUserList() {
return userList;
}
public void setUserList(List userList) {
this.userList = userList;
}
@Override
public String toString() {
return "Role{" +
"id=" + id +
", roleName='" + roleName + '\'' +
", roleDesc='" + roleDesc + '\'' +
", userList=" + userList +
'}';
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getRoleName() {
return roleName;
}
public void setRoleName(String roleName) {
this.roleName = roleName;
}
public String getRoleDesc() {
return roleDesc;
}
public void setRoleDesc(String roleDesc) {
this.roleDesc = roleDesc;
}
}
（4）测试类：
/*
* Copyright (c) 2020, 2023, All rights reserved.
*
*/
package com.by;
import com.by.mapper.AccountMapper;
import com.by.mapper.RoleMapper;
import com.by.mapper.UserMapper;
import com.by.pojo.Role;
import com.by.pojo.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
/**
* Project: mybatis - MyBatisTest
* Powered by scl On 2023-12-18 11:44:53
* 描述：
*
* @author 孙臣龙 [[email protected]]
* @version 1.0
* @since 17
*/
public class MyBatisTestRole {
private InputStream inputStream;
private SqlSession sqlSession;
@Before
public void init() throws IOException {
// 加载配置文件
String resource = "mybatis-config.xml";
inputStream = Resources.getResourceAsStream(resource);
// 创建sqlSessionFActory
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
// 获得数据的绘画实例
sqlSession = sessionFactory.openSession();
}
/**
* 多对多：一个人对应多个身份，一个身份包含不同的人
*
* @throws IOException
*/
@Test
public void findAllRoleByUser() {
RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
List allRoleByUser = roleMapper.findAllRoleByUser(45);
for (Role role : allRoleByUser) {
System.out.println(role);
}
}
@After
public void close() throws IOException {
inputStream.close();
sqlSession.close();
}
}
（5）结果展示：
