Mybatis學習筆記之---多表查詢(1)
阿新 • • 發佈：2019-08-14
Mybatis多表查詢（1）
（一）舉例（使用者和賬戶）
一個使用者可以有多個賬戶
一個賬戶只能屬於一個使用者(多個賬戶也可以屬於同一個使用者)
（二）步驟
1、建立兩張表:使用者表，賬戶表，讓使用者表和賬戶表之間具備一對多的關係:需要使用外來鍵在賬戶表中新增
2、建立兩個實體類:使用者實體類和賬戶實體類，讓使用者和賬戶的實體類能體現出來一對多的關係
3、建立兩個配置檔案，使用者的配置檔案賬戶的配置檔案
4、實現配置:當我們查詢使用者時，可以同時得到使用者下所包含的賬戶資訊當我們查詢賬戶時，可以同時得到賬戶的所屬使用者資訊
（三）程式碼實現
1.pom.xml
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.41</version>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.6</version>
</dependency>
</dependencies>
2.Users.java
package entity;
import java.util.List;
public class Users {
private int uid;
private String username;
private String password;
//一對多的關係對映，主表實體應該包含從表實體的集合引用
private List<Account> accounts;
public int getUid() {
return uid;
}
public void setUid(int uid) {
this.uid = uid;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public List<Account> getAccounts() {
return accounts;
}
public void setAccounts(List<Account> accounts) {
this.accounts = accounts;
}
@Override
public String toString() {
return accounts+
"uid=" + uid +
", username='" + username + '\'' +
", password='" + password + '\''
;
}
}
3.Account.java
package entity;
public class Account {
private int aid;
private String accountname;
private int uid;
private Users users;
public int getAid() {
return aid;
}
public void setAid(int aid) {
this.aid = aid;
}
public String getAccountname() {
return accountname;
}
public void setAccountname(String accountname) {
this.accountname = accountname;
}
public int getUid() {
return uid;
}
public void setUid(int uid) {
this.uid = uid;
}
public Users getUsers() {
return users;
}
public void setUsers(Users users) {
this.users = users;
}
@Override
public String toString() {
return
"aid=" + aid +
", accountname='" + accountname + '\'' +
", uid=" + uid
;
}
}
4.UsersAccount.java
package entity;
public class UsersAccount extends Account{
private String username;
private String password;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
@Override
public String toString() {
return "uid="+super.getUid()+",aid="+super.getAid()+", username='" + username + '\'' +
", password='" + password + '\'' +",accountname="+super.getAccountname();
}
}
5.SqlMapperConfig.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPEconfiguration
PUBLIC"-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--mybatis的主配置檔案-->
<configuration>
<!--配置環境-->
<environments default="mysql">
<!--配置mysql環境-->
<environment id="mysql">
<!--配置事務的型別-->
<transactionManager type="JDBC"></transactionManager>
<!--配置資料來源（連線池）-->
<dataSource type="POOLED">
<!--配置連線資料庫的4個基本資訊-->
<property name="driver" value="com.mysql.jdbc.Driver"></property>
<property name="url" value="jdbc:mysql://localhost:3306/zml01?useUnicode=true&characterEncoding=utf-8"></property>
<property name="username" value="root"></property>
<property name="password" value="root"></property>
</dataSource>
</environment>
</environments>
<!--指定對映配置檔案的位置，對映配置檔案指的是每個dao獨立的配置檔案-->
<mappers>
<mapper resource="dao/UserDao.xml"></mapper>
<mapper resource="dao/AccountDao.xml"></mapper>
</mappers>
</configuration>
6.UserDao.java
package dao;
import entity.Users;
import java.util.List;
public interface UserDao {
List<Users> findAll();
Users find(int id);
}
7.UserDao.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPEmapper
PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="dao.UserDao">
<!--定義Users的resultMap -->
<resultMap id="userAccountMap" type="entity.Users">
<id property="uid" column="uid"></id>
<result property="username" column="username"></result>
<result property="password" column="password"></result>
<!--配置Users物件中Account集合的對映,一對多的關係對映-->
<collection property="accounts" ofType="entity.Account">
<id property="aid" column="aid"></id>
<result property="accountname" column="accountname"></result>
<result property="uid" column="uid"></result>
</collection>
</resultMap>
<!--查詢所有,左外連線，返回左邊表的所有資料-->
<select id="findAll" resultMap="userAccountMap">
select * from users u left outer join account a on u.uid=a.uid
</select>
<!--根據ID查詢-->
<select id="find" resultType="entity.Users">
select * from users where uid=#{uid}
</select>
</mapper>
8.UserTest.java
package test;
import dao.UserDao;
import entity.Users;
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 UserTest {
private InputStream in;
private SqlSession sqlSession;
private UserDao UserDaoImpl;
@Before
public void init() throws IOException {
//1.讀取配置檔案
in= Resources.getResourceAsStream("SqlMapperConfig.xml");
//2.建立SqlSessionFactory工廠
SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();
SqlSessionFactory factory=builder.build(in);
//3.使用工廠生產SqlSession物件
sqlSession=factory.openSession();
//4.使用SqlSession建立dao介面的代理物件
UserDaoImpl=sqlSession.getMapper(UserDao.class);
}
@After
public void destroy() throws IOException {
//提交事務
sqlSession.commit();
//6.釋放資源
sqlSession.close();
in.close();
}
/**
* 查詢所有
* @throws IOException
*/
@Test
public void findall() throws IOException {
//5.使用代理物件執行方法
List<Users> users=UserDaoImpl.findAll();
for(Users u:users){
System.out.println(u);
}
}
}
9.AccountDao.java
package dao;
import entity.Account;
import entity.UsersAccount;
import java.util.List;
public interface AccountDao {
List<Account> findAll();
List<UsersAccount> find();
}
10.AccountDao.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPEmapper
PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="dao.AccountDao">
<!--定義封裝Account和Users的resultMap-->
<resultMap id="accountUsersMap" type="entity.Account">
<id property="aid" column="aid"></id>
<result property="accountname" column="accountname"></result>
<result property="uid" column="uid"></result>
<!--一對一的關係對映，配置封裝users的內容-->
<association property="users" column="uid" javaType="entity.Users">
<id property="uid" column="uid"></id>
<result property="username" column="username"></result>
<result property="password" column="password"></result>
</association>
</resultMap>
<!--查詢所有 ,內連線-->
<select id="findAll" resultMap="accountUsersMap">
select a.*,u.username,u.password from account a,users u where a.uid=u.uid
</select>
<select id="find" resultType="entity.UsersAccount">
select a.*,u.username,u.password from account a,users u where a.uid=u.uid
</select>
</mapper>
11.AccountTest.java
package test;
import dao.AccountDao;
import dao.UserDao;
import entity.Account;
import entity.Users;
import entity.UsersAccount;
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 AccountTest {
private InputStream in;
private SqlSession sqlSession;
private AccountDao AccountDaoImpl;
@Before
public void init() throws IOException {
//1.讀取配置檔案
in= Resources.getResourceAsStream("SqlMapperConfig.xml");
//2.建立SqlSessionFactory工廠
SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();
SqlSessionFactory factory=builder.build(in);
//3.使用工廠生產SqlSession物件
sqlSession=factory.openSession();
//4.使用SqlSession建立dao介面的代理物件
AccountDaoImpl=sqlSession.getMapper(AccountDao.class);
}
@After
public void destroy() throws IOException {
//提交事務
sqlSession.commit();
//6.釋放資源
sqlSession.close();
in.close();
}
/**
* 查詢所有
* @throws IOException
*/
@Test
public void findall() throws IOException {
//5.使用代理物件執行方法
List<Account> account=AccountDaoImpl.findAll();
for(Account a:account){
System.out.println(a);
System.out.println(a.getUsers());
}
}
/**
* 查詢使用者的所有訂單
* @throws IOException
*/
@Test
public void find() throws IOException {
//5.使用代理物件執行方法
List<UsersAccount> ua=AccountDaoImpl.find();
for(UsersAccount a:ua){
System.out.println(a);
}
}
}
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