mybatis sqlite 两个数据库 mybatis两个表联合查询

1、 项目简介

首先呢，我们创建两张表，一个是users表，一个是account表，两张表组成了用户和账户之间的关系，一个用户可以有多个账户，一个账户只能属于一个用户，这就是我们的背景。首先实现一对一表的联合查询，一个用户对应一张表。

2、数据库表

用户表users

账户表account

中账户表的uid为外键，指向的是用户表的主键id

3、项目的目录

4、我们首先来看两个实体类，对应着两张表

1、User类

public class User implements Serializable {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

2、Account类：这里需要注意的是，在这里定义了一User的类。用于查询当前账户所属的用户信息。

public class Account implements Serializable {
    private Integer id;
    private  Integer uid;
    private String money;
    private  User user;

5、查看咱们的主要配置文件：IAccountDao.xml

在之前的文章中提到过resultMap这个标签，但是对于多表查询我们还需要嵌套一个association标签。因为我们主要查询的是账户信息，其次是附带的用户信息，所以将用户信息放在association标签内。其中的property就是咱们在Account类中定义的属性。接着就是SQL语句select u.*,a.id as aid,a.uid,a.money from account a,users u where u.id = a.uid。我们首先将两张表分别取别名，然后条件是id与uid相等，之后我们先查询出用户的所有信息，然后查询出账户的信息，哪张表放在前面都行。

<?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.mybatis.dao.IAccountDao">
<!--    定义封装account和user的resultMap-->
    <resultMap id="accountUserMap" type="com.mybatis.domain.Account">
        <id property="id" column="aid"></id>
        <result property="uid" column="uid"></result>
        <result property="money" column="money"></result>
<!--        一对一关系映射，配置封装user的内容-->
        <association property="user" column="uid">
            <id property="id" column="id"></id>
            <result property="username" column="username"></result>
            <result property="address" column="address"></result>
            <result property="sex" column="sex"></result>
            <result property="birthday" column="birthday"></result>
        </association>
    </resultMap>
<!--    查询所有-->
    <select id="findAll" resultMap="accountUserMap">
        select u.*,a.id as aid,a.uid,a.money from account a,users u where u.id = a.uid
    </select>
</mapper>

5、运行

public  void testFindAll() throws Exception{
        List<Account> accounts = accountDao.findAll();
        for (Account a:accounts){
            System.out.println("-----------------------");
            System.out.println(a + " "+ a.getUser());
        }
    }

6、全部源代码

Account类：

package com.mybatis.domain;

import java.io.Serializable;

public class Account implements Serializable {
    private Integer id;
    private  Integer uid;
    private String 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 String getMoney() {
        return money;
    }

    public void setMoney(String money) {
        this.money = money;
    }

    @Override
    public String toString() {
        return "Account{" +
                "id=" + id +
                ", uid=" + uid +
                ", money='" + money + '\'' +
                '}';
    }
}

User类

package com.mybatis.domain;

import java.io.Serializable;
import java.util.Date;

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 + '\'' +
                '}';
    }
}

IAccountDao接口

package com.mybatis.dao;

import com.mybatis.domain.Account;

import java.util.List;

public interface IAccountDao {
    /**
     * 查询所有的Account
     * @return
     */
    List<Account> findAll();

}

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="com.mybatis.dao.IAccountDao">
<!--    定义封装account和user的resultMap-->
    <resultMap id="accountUserMap" type="com.mybatis.domain.Account">
        <id property="id" column="aid"></id>
        <result property="uid" column="uid"></result>
        <result property="money" column="money"></result>
<!--        一对一关系映射，配置封装user的内容-->
        <association property="user" column="uid">
            <id property="id" column="id"></id>
            <result property="username" column="username"></result>
            <result property="address" column="address"></result>
            <result property="sex" column="sex"></result>
            <result property="birthday" column="birthday"></result>
        </association>
    </resultMap>
<!--    查询所有-->
    <select id="findAll" resultMap="accountUserMap">
        select u.*,a.id as aid,a.uid,a.money from account a,users u where u.id = a.uid
    </select>
</mapper>

SqlMapConfig.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--mybatis主配置文件-->
<configuration>
    <!--配置环境-->
    <environments default="mysql">
<!--        配置mysql环境-->
        <environment id="mysql">
<!--            配置事务类型-->
            <transactionManager type="JDBC"></transactionManager>
<!--            配置数据源（连接池）-->
            <dataSource type="POOLED">
<!--                配置数据库的基本信息-->
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?serverTimezone=GMT"/>
                <property name="username" value="root"/>
                <property name="password" value="111111"/>
            </dataSource>
        </environment>
    </environments>
<!--    指定映射配置文件的位置，映射配置文件指的是每一个dao独立的配置文件-->
    <mappers>
        <package name="com.mybatis.dao"/>
    </mappers>

</configuration>

测试类

package com.mybatis.test;


import com.mybatis.dao.IAccountDao;
import com.mybatis.dao.IUserDao;
import com.mybatis.domain.Account;
import com.mybatis.domain.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;

public class MybatisAccountTest {
    private InputStream  in;
    private SqlSession session;
    private IAccountDao accountDao;

    @Before
    public void init() throws Exception {
        this.in = Resources.getResourceAsStream("SqlMapConfig.xml");
        SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();
        System.out.println(in);
        SqlSessionFactory factory = factoryBuilder.build(in);
//        this.session = factory.openSession(true);
        this.session = factory.openSession();
        this.accountDao = session.getMapper(IAccountDao.class);
    }
    @After
    public void destory() throws IOException {
        session.commit();
        this.in.close();
        this.session.close();
    }
    @Test
    public  void testFindAll() throws Exception{
        List<Account> accounts = accountDao.findAll();
        for (Account a:accounts){
            System.out.println("-----------------------");
            System.out.println(a + " "+ a.getUser());
        }
    }
}