MyBatis07_多表查询一
本教程源码请访问:tutorial_demo
之前的教程中,我们学习了MyBatis的单表CRUD,在实际的项目中,很多时候要用到多表的查询,今天我们就来学习一下,这篇教程用到的数据库脚本、pom.xml、SqlMapConfig.xml和《02_MyBatis快速入门》中是完全一样的,大家需要在这篇文章的基础上进行学习。本案例分析“一对一”、“一对多”关系时,使用用户表(user)和账户表(account)来分析。
一、一对一查询
因为一个账户信息只能供某个用户使用,所以从查询账户信息(account)出发关联查询用户信息(user)为一对一查询。如果从用户信息(user)出发查询用户下的账户信息(account)则为一对多查询,因为一个用户可以有多个账户 。
1.1、方式一
1.1.1、定义账户信息的实体类(Account)
package org.codeaction.domain;
import java.io.Serializable;
public class Account implements Serializable {
private Integer id;
private Integer uid;
private Double money;
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;
}
@Override
public String toString() {
return "Account{" +
"id=" + id +
", uid=" + uid +
", money=" + money +
'}';
}
}
1.1.2、定义包含账户信息及用户信息的类(AccountUser)
package org.codeaction.domain;
import java.io.Serializable;
import java.util.Date;
public class AccountUser extends Account implements Serializable {
private String username;
private String sex;
private String address;
private Date birthday;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
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;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
@Override
public String toString() {
return super.toString() + " AccountUser{" +
"username='" + username + '\'' +
", sex='" + sex + '\'' +
", address='" + address + '\'' +
", birthday=" + birthday +
'}';
}
}
1.1.3、SQL语句
select
a.*, u.username username, u.sex sex, u.address address, u.birthday birthday
from
account a, user u
where
a.uid = u.id;
1.1.4、定义持久层Dao接口
package org.codeaction.dao;
import org.codeaction.domain.AccountUser;
import java.util.List;
public interface IAccountDao {
List<AccountUser> findAll();
}
1.1.5、定义IAccountDao.xml
<?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="org.codeaction.dao.IAccountDao">
<!-- 配置查询所有 -->
<select id="findAll" resultType="org.codeaction.domain.AccountUser">
select
a.*, u.username username, u.sex sex, u.address address, u.birthday birthday
from
account a, user u
where
a.uid = u.id;
</select>
</mapper>
1.1.6、定义测试类
package org.codeaction.test;
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.codeaction.dao.IAccountDao;
import org.codeaction.domain.AccountUser;
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 MyBatisTest {
private InputStream in;
private SqlSession session;
@Before
public void init() throws IOException {
//读取配置文件
in = Resources.getResourceAsStream("SqlMapConfig.xml");
//创建SqlSessionFactory工厂
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(in);
//使用工厂生产SqlSession对象
session = factory.openSession();
}
@After
public void destroy() throws IOException {
//提交事务
session.commit();
//释放资源
session.close();
in.close();
}
@Test
public void testFindAll() {
IAccountDao accountDao = session.getMapper(IAccountDao.class);
List<AccountUser> list = accountDao.findAll();
list.forEach(System.out::println);
}
}
运行测试方法,输出如下:
Account{id=1, uid=41, money=1000.0} AccountUser{username='王一', sex='男', address='北京', birthday=Tue Dec 27 17:47:08 CST 2011}
Account{id=2, uid=45, money=1000.0} AccountUser{username='Max', sex='男', address='西宁', birthday=Tue May 04 12:04:06 CST 2010}
Account{id=3, uid=41, money=2000.0} AccountUser{username='王一', sex='男', address='北京', birthday=Tue Dec 27 17:47:08 CST 2011}
专门定义类作为输出类型,这种方式使用普遍。
1.2、方式二
使用resultMap,定义专门的resultMap用于映射一对一的查询结果。
1.2.1、修改账户信息的实体类(Account)
在Account类中加入User类的对象作为Account类的一个属性(User类的定义参考《02_MyBatis快速入门》)。
package org.codeaction.domain;
import java.io.Serializable;
public class Account implements Serializable {
private Integer id;
private Integer uid;
private Double money;
private 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;
}
@Override
public String toString() {
return "Account{" +
"id=" + id +
", uid=" + uid +
", money=" + money +
", user=" + user +
'}';
}
}
1.2.2、修改持久层Dao接口
package org.codeaction.dao;
import org.codeaction.domain.Account;
import org.codeaction.domain.AccountUser;
import java.util.List;
public interface IAccountDao {
List<AccountUser> findAll();
List<Account> findAll1();
}
1.2.3、修改IAccountDao.xml
<?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="org.codeaction.dao.IAccountDao">
<resultMap id="AccountUser" type="org.codeaction.domain.Account">
<id property="id" column="aid" />
<result property="uid" column="uid" />
<result property="money" column="money" />
<association property="user" column="uid">
<id property="id" column="id" />
<result property="username" column="username" />
<result property="birthday" column="birthday" />
<result property="sex" column="sex" />
<result property="address" column="address" />
</association>
</resultMap>
<!-- 配置查询所有 -->
<select id="findAll" resultType="org.codeaction.domain.AccountUser">
select
a.*, u.username username, u.sex sex, u.address address, u.birthday birthday
from
account a, user u
where
a.uid = u.id;
</select>
<!-- 配置查询所有 -->
<select id="findAll1" resultMap="AccountUser">
select
a.id aid, a.uid uid, a.money money, u.*
from
account a, user u
where
a.uid = u.id;
</select>
</mapper>
1.2.4、添加测试方法
@Test
public void testFindAll1() {
IAccountDao accountDao = session.getMapper(IAccountDao.class);
List<Account> list = accountDao.findAll1();
list.forEach(System.out::println);
}
二、一对多查询
用户信息和账户信息是一对多的关系,一个用户可以对应多个账户,查询过程中如果用户没有账户信息,此时也要将用户信息查询出来,我们想到了左外连接查询比较合适。
2.1、修改User类
package org.codeaction.domain;
import java.io.Serializable;
import java.util.Date;
import java.util.List;
public class User implements Serializable {
private Integer id;
private String username;
private Date birthday;
private String sex;
private String address;
private List<Account> accounts;
public List<Account> getAccounts() {
return accounts;
}
public void setAccounts(List<Account> accounts) {
this.accounts = accounts;
}
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 + '\'' +
", accounts=" + accounts +
'}';
}
}
2.2、定义持久层Dao接口
package org.codeaction.dao;
import org.codeaction.domain.User;
import java.util.List;
public interface IUserDao {
List<User> findAllUser();
}
2.3、定义IUserDao.xml
<?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="org.codeaction.dao.IUserDao">
<resultMap id="userAccountMap" type="org.codeaction.domain.User">
<id property="id" column="id"></id>
<result property="username" column="username"></result>
<result property="birthday" column="birthday"></result>
<result property="sex" column="sex"></result>
<result property="address" column="address"></result>
<!--
collection:是用于建立一对多中集合属性的对应关系
property:关联结果存储在哪个属性
ofType:用于指定集合元素的数据类型
-->
<collection property="accounts" ofType="org.codeaction.domain.Account">
<id property="id" column="aid"></id>
<result property="money" column="money"></result>
<result property="uid" column="uid"></result>
</collection>
</resultMap>
<!-- 配置查询所有 -->
<select id="findAllUser" resultMap="userAccountMap">
select
u.*, a.id aid, a.MONEY money, a.UID uid
from
user u left join account a
on
u.id = a.UID;
</select>
</mapper>
2.4、添加测试方法
@Test
public void testFindAllUser() {
IUserDao userDao = session.getMapper(IUserDao.class);
List<User> list = userDao.findAllUser();
list.forEach(System.out::println);
}
运行测试方法,控制台输出如下
User{id=41, username='王一', birthday=Tue Dec 27 17:47:08 CST 2011, sex='男', address='北京', accounts=[Account{id=1, uid=41, money=1000.0, user=null}, Account{id=3, uid=41, money=2000.0, user=null}]}
User{id=45, username='Max', birthday=Tue May 04 12:04:06 CST 2010, sex='男', address='西宁', accounts=[Account{id=2, uid=45, money=1000.0, user=null}]}
User{id=42, username='王二', birthday=Sat Mar 12 15:09:37 CST 2011, sex='女', address='上海', accounts=[]}
User{id=43, username='老李', birthday=Wed Mar 14 11:34:34 CST 2012, sex='女', address='天津', accounts=[]}
User{id=46, username='老王', birthday=Sat Aug 07 17:37:26 CST 1999, sex='女', address='拉萨', accounts=[]}
User{id=48, username='John', birthday=Mon Jan 08 11:44:00 CST 1990, sex='女', address='广州', accounts=[]}
User{id=50, username='Lucy', birthday=Wed Dec 03 20:09:32 CST 2008, sex='m', address='哈尔滨', accounts=[]}
User{id=58, username='张三', birthday=Fri May 15 18:50:04 CST 2020, sex='男', address='南昌', accounts=[]}
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