使用Mybatis进行多表联查操作

（1）增加一个测试数据库shop_order，sql语句如下：

CREATE DATABASE `shop_order`;

USE `shop_order`;

CREATE TABLE `t_user` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `username` VARCHAR(20) DEFAULT NULL,
  `password` VARCHAR(50) DEFAULT NULL,
  `sex` VARCHAR(2) DEFAULT NULL,
  `brithday` DATE DEFAULT NULL,
  `address` VARCHAR(200) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=INNODB AUTO_INCREMENT=20 DEFAULT CHARSET=utf8;

CREATE TABLE `t_product` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `name` VARCHAR(100) DEFAULT NULL,
  `price` FLOAT DEFAULT NULL,
  `description` TEXT,
  PRIMARY KEY (`id`)
) ENGINE=INNODB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;

CREATE TABLE `t_order` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `userId` INT(11) DEFAULT NULL,
  `createTime` DATETIME DEFAULT NULL,
  `state` VARCHAR(20) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fk_userId` (`userId`),
  CONSTRAINT `fk_userId` FOREIGN KEY (`userId`) REFERENCES `t_user` (`id`)
) ENGINE=INNODB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

CREATE TABLE `t_orderdetail` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `productId` INT(11) DEFAULT NULL,
  `orderId` INT(11) DEFAULT NULL,
  `num` INT(11) DEFAULT NULL,
  `price` FLOAT DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fk_productId` (`productId`),
  KEY `fk_orderId` (`orderId`),
  CONSTRAINT `fk_orderId` FOREIGN KEY (`orderId`) REFERENCES `t_order` (`id`),
  CONSTRAINT `fk_productId` FOREIGN KEY (`productId`) REFERENCES `t_product` (`id`)
) ENGINE=INNODB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

INSERT  INTO `t_user`(`id`,`username`,`password`,`sex`,`brithday`,`address`) VALUES (16,'小黄','2222','男','2014-01-01','中国'),(17,'陌拜','1100','男','2014-03-03','深圳'),(18,'本拉登','9999','男','2003-09-09','印度'),(19,'奥巴马小号','1399','男','2005-01-09','美国');

INSERT  INTO `t_product`(`id`,`name`,`price`,`description`) VALUES (6,'飞机',20000000,'预售，提货时间暂定'),(7,'坦克',300000000,'预售，提货时间暂定'),(8,'大炮',500000,'预售，提货时间暂定'),(9,'航母',900000000,'预售，提货时间暂定');

INSERT  INTO `t_order`(`id`,`userId`,`createTime`,`state`) VALUES (1,18,'2015-07-04 00:00:00','已付'),(2,19,'2017-01-02 00:00:00','已付'),(3,16,'2017-12-13 10:07:21','待付'),(4,18,'2017-12-05 14:44:04','报废');

INSERT  INTO `t_orderdetail`(`id`,`productId`,`orderId`,`num`,`price`) VALUES (1,8,1,6,3000000),(2,9,2,1,900000000),(3,6,NULL,NULL,NULL);

（2）建立程序的结构，结构如下

（3）建立实体类，与数据库中的表对应

Order.java代码如下：

package entity;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;


public class Order {
    private int id;
    private Date userId;
    private String createTime;
    private String state;
　　//注意这里报错是正常的，因为这里之后引用了其他的实体类，它们还没被定义，把所有的实体类建立好了以后，保存一下就可以了
    private User user;        //一个订单对应一个用户，所以在订单中放置一个User的对象
    //一个订单可以有多件商品，这里对应多个商品详情，所以放置一个商品详情集合
    private List<OrderDetail> orderDetails = new ArrayList<OrderDetail>();
    public Order() {
        super();
    }
    public Order(int id, Date userId, String createTime, String state) {
        super();
        this.id = id;
        this.userId = userId;
        this.createTime = createTime;
        this.state = state;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public Date getUserId() {
        return userId;
    }
    public void setUserId(Date userId) {
        this.userId = userId;
    }
    public String getCreateTime() {
        return createTime;
    }
    public void setCreateTime(String createTime) {
        this.createTime = createTime;
    }
    public String getState() {
        return state;
    }
    public void setState(String state) {
        this.state = state;
    }
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
    public List<OrderDetail> getOrderDetails() {
        return orderDetails;
    }
    public void setOrderDetails(List<OrderDetail> orderDetails) {
        this.orderDetails = orderDetails;
    }
}

OrderDetail.java类的代码如下：

package entity;

public class OrderDetail {
    private int id;
    private int productId;
    private int orderId;
    private double price;
    private int num;
    private Order order;   //一个订单详情，对应某一个订单，所有在这里添加一个订单对象
    private Product product;    //一个订单详情里面存放一种商品，对应一个商品详情
    public OrderDetail() {
        super();
    }
    public OrderDetail(int id, int productId, int orderId, double price, int num) {
        super();
        this.id = id;
        this.productId = productId;
        this.orderId = orderId;
        this.price = price;
        this.num = num;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public double getPrice() {
        return price;
    }
    public void setPrice(double price) {
        this.price = price;
    }
    public int getNum() {
        return num;
    }
    public void setNum(int num) {
        this.num = num;
    }
    public Order getOrder() {
        return order;
    }
    public void setOrder(Order order) {
        this.order = order;
    }
    public int getProductId() {
        return productId;
    }
    public void setProductId(int productId) {
        this.productId = productId;
    }
    public int getOrderId() {
        return orderId;
    }
    public void setOrderId(int orderId) {
        this.orderId = orderId;
    }
    public Product getProduct() {
        return product;
    }
    public void setProduct(Product product) {
        this.product = product;
    }
}

Product.java类代码

package entity;

public class Product {
    private int id;
    private String name;
    private float price;
    private String description;
    public Product() {
        super();
    }
    public Product(int id, String name, float price, String description) {
        super();
        this.id = id;
        this.name = name;
        this.price = price;
        this.description = description;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public float getPrice() {
        return price;
    }
    public void setPrice(float price) {
        this.price = price;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }
}

User.java类的代码如下：

package entity;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;

public class User {
    private int id;
    private String username;
    private String password;
    private String sex;
    private Date brithday;
    private String address;
    private List<Order> orders = new ArrayList<Order>();
    public User() {
        super();
    }
    public User(int id, String username, String password, String sex,
            Date brithday, String address) {
        super();
        this.id = id;
        this.username = username;
        this.password = password;
        this.sex = sex;
        this.brithday = brithday;
        this.address = address;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    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 String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public Date getBrithday() {
        return brithday;
    }
    public void setBrithday(Date brithday) {
        this.brithday = brithday;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    public List<Order> getOrders() {
        return orders;
    }
    public void setOrders(List<Order> orders) {
        this.orders = orders;
    }
}

（4）编写mybatis-config.xml文件

<?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">
<!-- 配置文件的根元素  -->
<configuration>        
    <!-- 环境：配置mybatis的环境  -->
    <environments default="development">    <!-- 可以使用多个环境变量，切换时只需修改对应default的属性为该环境变量的id即可  -->
        <!-- 环境变量：可以配置多个环境变量，比如使用多数据源时，就需要配置多个环境变量 -->
        <environment id="development">
            <!-- 事务管理 -->
            <transactionManager type="JDBC"></transactionManager>
            <!-- 数据源 -->
            <dataSource type="POOLED">
                <property name="username" value="root" />
                <property name="url" value="jdbc:mysql://localhost:3306/shop_order" />
                <property name="password" value="123" />
                    <!-- 定义驱动连接,根据所使用的数据库的不同进行更换，作者使用的是mySql -->
                <property name="driver" value="com.mysql.jdbc.Driver" />
            </dataSource>
        </environment>
    </environments>    
</configuration>

（5）编写SqlSessionUtil.java拿到数据库的操作对象SqlSession，代码如下

package common;

import java.io.IOException;
import java.io.InputStream;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class SqlSessionUtil {
    public static SqlSession getSession(){
        InputStream input = null;
        try {
            input = Resources.getResourceAsStream("mybatis-config.xml");
        } catch (IOException e) {
            e.printStackTrace();
        }
        SqlSessionFactoryBuilder builder =new SqlSessionFactoryBuilder();
        SqlSessionFactory sqlSessionFactory=builder.build(input);
        SqlSession session=sqlSessionFactory.openSession();
        return session;
    }
}

 （6）编写dao里面的接口，这边学习就只写了两个，里面的方法也很简单

OrderDao.java

package dao;

import java.util.List;

import entity.Order;

public interface OrderDao {

    /**
     * 查询所有的订单，并取出该订单的用户信息
     * @return
     */
    List<Order> queryAllOrder();
}

 UserDao.java

package dao;

import java.util.List;

import entity.User;

public interface UserDao {
    
    /**
     * 查询所有用户，并显示每个用户的订单
     * @return
     */
    List<User> queryAllUser();
}

（7）编写mapper里面的xml文件，里面存放数据库语句

OrderMapper.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="dao.OrderDao">
  
      <select id="queryAllOrder" resultMap="Order_User">
          select *,od.id as o_id,us.id as u_id from t_order as od inner join t_user as us on od.userId=us.id 
      </select>
      
      <resultMap type="entity.Order" id="Order_User">
          <id column="o_id" property="id"/>
          <result column="userId" property="userId"/>
          <result column="createTime" property="createTime"/>
          <result column="state" property="state"/>
          <association property="user" javaType="entity.User">
          <id column="u_id" property="id"></id>
          <result column="username" property="username"/>
          <result column="password" property="password"/>
          <result column="sex" property="sex"/>
          <result column="brithday" property="brithday"/>
          <result column="address" property="address"/>
          </association>
      </resultMap>        
  </mapper>

UserMapper.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="dao.UserDao">
      <resultMap type="entity.User" id="User_Order">
          <id column="id" property="id"/>
          <result column="username" property="username"/>
          <result column="password" property="password"/>
          <result column="sex" property="sex"/>
          <result column="brithday" property="brithday"/>
          <result column="address" property="address"/>
          
          <collection property="orders" ofType="entity.Order">
              <id column="o_id" property="id"/>
              <result column="userId" property="userId"/>
              <result column="createTime" property="createTime"/>
              <result column="state" property="state"/>
          </collection>
      </resultMap>
  
      <select id="queryAllUser" resultMap="User_Order">
          SELECT *,o.id AS o_id FROM t_user AS u INNER JOIN t_order AS o ON u.id=o.userId
      </select>
  </mapper>

（8）在mybatis-config.xml中的<configuration>标签里面<environments>标签下面添加如下映射

<mappers>
        <mapper resource="mapper/UserMapper.xml"/><!-- 包名。xml文件名 -->
        <!-- <mapper resource="mapper/OrderMapper.xml"></mapper> -->
    </mappers>

（9）编写方法测试

test.java

package text;

import java.util.List;

import org.apache.ibatis.session.SqlSession;

import common.SqlSessionUtil;
import dao.OrderDao;
import dao.UserDao;
import entity.Order;
import entity.User;

public class test {
    
    public static void main(String[] args) {
        SqlSession session = SqlSessionUtil.getSession();//获取数据库操作对象SqlSession
        UserDao userDao = session.getMapper(dao.UserDao.class);
        List<User> users = userDao.queryAllUser();
        for (User user : users) {
            System.out.println("用户："+user.getUsername()+"的订单");
            for (Order order : user.getOrders()) {
                System.out.println("订单编号："+order.getId());
                System.out.println("状态:"+order.getState());
            }
            System.out.println();
        }
        
        
        System.out.println("///////////////////////////////////");
        System.out.println();
        OrderDao orderdao = session.getMapper(dao.OrderDao.class);
        List<Order> orders = orderdao.queryAllOrder();
        for (Order order : orders) {
            System.out.println("订单编号："+order.getId());
            System.out.println("购买者："+order.getUser().getUsername());
            System.out.println("订单状态："+order.getState());
            System.out.println();
        }
　　　　session.close();　　//回收session,刷新缓冲区；
    }
}