Mybatis学习笔记之---多表查询(1)

时间：2021-11-28 23:16:02

Mybatis多表查询（1）

（一）举例（用户和账户）

一个用户可以有多个账户
一个账户只能属于一个用户(多个账户也可以属于同一个用户)

（二）步骤

1、建立两张表:用户表，账户表，让用户表和账户表之间具备一对多的关系:需要使用外键在账户表中添加

2、建立两个实体类:用户实体类和账户实体类，让用户和账户的实体类能体现出来一对多的关系

3、建立两个配置文件，用户的配置文件账户的配置文件

4、实现配置:当我们查询用户时，可以同时得到用户下所包含的账户信息当我们查询账户时，可以同时得到账户的所属用户信息

（三）代码实现

Mybatis学习笔记之---多表查询(1)

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;

    //一对多的关系映射，主表实体应该包含从表实体的集合引用

    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的主配置文件-->

<configuration>

    <!--配置环境-->

    <environments default="mysql">

        <!--配置mysql环境-->

        <environment id="mysql">

            <!--配置事务的类型-->

            <transactionManager type="JDBC"></transactionManager>

            <!--配置数据源（连接池）-->

            <dataSource type="POOLED">

                <!--配置连接数据库的4个基本信息-->

                <property name="driver" value="com.mysql.jdbc.Driver"></property>

                <property name="url" value="jdbc:mysql://localhost:3306/zml01?useUnicode=true&amp;characterEncoding=utf-8"></property>

                <property name="username" value="root"></property>

                <property name="password" value="root"></property>

            </dataSource>

        </environment>

    </environments>

    <!--指定映射配置文件的位置，映射配置文件指的是每个dao独立的配置文件-->

<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">

    <!--定义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对象中Account集合的映射,一对多的关系映射-->

        <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>

    <!--查询所有,左外连接，返回左边表的所有数据-->

    <select id="findAll" resultMap="userAccountMap">

        select * from users u left outer join account a on u.uid=a.uid

    </select>

    <!--根据ID查询-->

    <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.读取配置文件

        in= Resources.getResourceAsStream("SqlMapperConfig.xml");

        //2.创建SqlSessionFactory工厂

        SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();

        SqlSessionFactory factory=builder.build(in);

        //3.使用工厂生产SqlSession对象

        sqlSession=factory.openSession();

        //4.使用SqlSession创建dao接口的代理对象

        UserDaoImpl=sqlSession.getMapper(UserDao.class);

    }

    @After

    public void destroy() throws IOException {

        //提交事务

        sqlSession.commit();

        //6.释放资源

        sqlSession.close();

        in.close();

    }

    /**

     * 查询所有

     * @throws IOException

     */

    @Test

    public void findall() throws IOException {

        //5.使用代理对象执行方法

        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">

    <!--定义封装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>

        <!--一对一的关系映射，配置封装users的内容-->

        <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>

    <!--查询所有 ,内连接-->

    <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.读取配置文件

        in= Resources.getResourceAsStream("SqlMapperConfig.xml");

        //2.创建SqlSessionFactory工厂

        SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();

        SqlSessionFactory factory=builder.build(in);

        //3.使用工厂生产SqlSession对象

        sqlSession=factory.openSession();

        //4.使用SqlSession创建dao接口的代理对象

        AccountDaoImpl=sqlSession.getMapper(AccountDao.class);

    }

    @After

    public void destroy() throws IOException {

        //提交事务

        sqlSession.commit();

        //6.释放资源

        sqlSession.close();

        in.close();

    }

    /**

     * 查询所有

     * @throws IOException

     */

    @Test

    public void findall() throws IOException {

        //5.使用代理对象执行方法

        List<Account> account=AccountDaoImpl.findAll();

        for(Account a:account){

            System.out.println(a);

            System.out.println(a.getUsers());

        }

    }

    /**

     * 查询用户的所有订单

     * @throws IOException

     */

    @Test

    public void find() throws IOException {

        //5.使用代理对象执行方法

        List<UsersAccount> ua=AccountDaoImpl.find();

        for(UsersAccount a:ua){

            System.out.println(a);

        }

    }

}

相关文章