mybatis一对多查询

mybatis一对多查询

需求：查询所有用户信息及用户关联的账户信息。

分析：用户信息和他的账户信息为一对多关系，并且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

1、编写sql语句

SELECT * FROM USER u LEFT OUTER JOIN account a ON u.`id`=a.`UID`

2、用户实体类

package com.yl.bean;

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

/**
 * 用户实体类
 */
public class User implements Serializable {
    private Integer id;//id
    private String username;//用户名
    private Date birthday;//生日
    private String sex;//性别
    private String address;//地址
    private List<Account> accountList;//用户所拥有的账户

    public User() {
    }

    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;
    }

    public List<Account> getAccountList() {
        return accountList;
    }

    public void setAccountList(List<Account> accountList) {
        this.accountList = accountList;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", birthday=" + birthday +
                ", sex='" + sex + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

3、账户实体类

package com.yl.bean;

import java.io.Serializable;

/**
 * 账户实体类
 */
public class Account implements Serializable {
    private Integer id;//账户id
    private Integer uid;//用户id
    private Double money;//余额
    private User user;//账户所属用户

    public Account() {
    }

    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;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

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

4、用户持久层接口

package com.yl.dao;

import com.yl.bean.User;

import java.util.List;

/**
 * 用户持久层接口
 */
public interface IUserDao {

    /**
     * 查询所有用户
     */
    List<User> queryAll();
}

5、用户配置文件

<?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.yl.dao.IUserDao">
    <!--配置用户实体类和数据库的对应信息-->
    <resultMap id="userMap" type="com.yl.bean.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>
        <!--一对多映射关系-->
        <collection property="accountList" ofType="com.yl.bean.Account">
            <id property="id" column="id"></id>
            <result property="uid" column="uid"></result>
            <result property="money" column="money"></result>
        </collection>
    </resultMap>

    <!--查询所有用户-->
    <select id="queryAll" resultMap="userMap">
        SELECT * FROM USER u LEFT OUTER JOIN account a ON u.`id`=a.`UID`
    </select>
</mapper>

6、测试

package com.yl;

import com.yl.bean.User;
import com.yl.dao.IUserDao;
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.sql.Date;
import java.util.List;


public class UserTest {
    private InputStream inputStream;
    private IUserDao userDao;
    private SqlSession sqlSession;

    @Before
    public void init() throws IOException {
        //读取配置文件
        inputStream= Resources.getResourceAsStream("SqlMapperConfig.xml");
        //创建工厂
        SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory sessionFactory= factoryBuilder.build(inputStream);
        //创建SqlSession对象
        sqlSession=sessionFactory.openSession();
        //创建IUserDao接口代理对象
        userDao=sqlSession.getMapper(IUserDao.class);
    }

    @After
    public void after() throws IOException {
        //提交事务
        sqlSession.commit();;
        //关闭资源
        sqlSession.close();
        inputStream.close();
    }

    /**
     * 查询所有
     */
    @Test
    public void test01() throws IOException {
        //查询所有用户
        List<User> userList=userDao.queryAll();
        //遍历输出
        for (User user:userList){
            System.out.println(user);
            System.out.println(user.getAccountList());
        }
    }

}