Mybatis学习之一对多关联查询

消费者和订单是典型的一对多关系，以此模型来学习mybatis的一对多关联查询 

配置文件定义：

<?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">
<configuration>
	<typeAliases>
		<typeAlias alias="Customer" type="com.mybatis.bean.Customer"/>
		<typeAlias alias="Order" type="com.mybatis.bean.Order"/>
	</typeAliases>
	<!--数据库参数配置 -->
	<environments default="development">
		<environment id="development">
			<transactionManager type="JDBC" />
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url" value="jdbc:mysql://localhost:3306/test" />
				<property name="username" value="root" />
				<property name="password" value="root" />
			</dataSource>
		</environment>
	</environments>
	<mappers>
		<mapper resource="com/mybatis/bean/Customer.xml" />
		<mapper resource="com/mybatis/bean/Order.xml" />
	</mappers>
</configuration>

　　简单封装sqlSessionFactory

package com.mybatis.util;

import java.io.IOException;
import java.io.Reader;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class MybatisUtil {
	private static SqlSessionFactory sqlSessionFactory;

	public static SqlSessionFactory getSqlSessionFactory() throws IOException {
		if (sqlSessionFactory == null) {
			String resource = "mybatis-config.xml";
			Reader reader = Resources.getResourceAsReader(resource);
			sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
		}
		return sqlSessionFactory;
	}
}

　　消费者bean对象定义：

package com.mybatis.bean;

import java.util.List;

public class Customer {

	private int id;

	private String name;

	private List<Order> orderList;

	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 List<Order> getOrderList() {
		return orderList;
	}

	public void setOrderList(List<Order> orderList) {
		this.orderList = orderList;
	}

}

　　订单bean对象定义：

package com.mybatis.bean;

public class Order {

	private int id;

	private int price;

	private String name;

	private Customer customer;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public int getPrice() {
		return price;
	}

	public void setPrice(int price) {
		this.price = price;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Customer getCustomer() {
		return customer;
	}

	public void setCustomer(Customer customer) {
		this.customer = customer;
	}

}

　　消费者SQL映射文件定义，一个消费者者可以对应多个订单，所以在定义resultMap时，要用到collection

<?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.inter.ICustomerDAO">

	<resultMap type="Customer" id="cumtomerResMap">
		<id property="id" column="c_id" />
		<result property="name" column="c_name" />
		<collection property="orderList" ofType="Order" column="cid">
			<id property="id" column="o_id" />
			<result property="name" column="o_name" />
			<result property="price" column="o_price" />
		</collection>
	</resultMap>

	<select id="selectCustomer" resultMap="cumtomerResMap">
		select * from customer
		c,orders o where o.cid=c.c_id and c.c_id=#{id}
	</select>
</mapper>

　　订单SQL映射文件定义，一个订单只能对应一个消费者，所以在定义resultMap时，要用到association

<?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.inter.IOrderDAO">
	<resultMap type="Order" id="orderResMap">
		<id property="id" column="o_id" />
		<result property="name" column="o_name" />
		<result property="price" column="o_price" />
		<association property="customer" javaType="Customer">
			<id property="id" column="c_id" />
			<result property="name" column="c_name" />
		</association>
	</resultMap>

	<select id="selectOrder" resultMap="orderResMap">
		select * from customer
		c,orders o where o.cid=c.c_id and o.o_id=#{id}
	</select>
</mapper>

　　消费者mapper接口定义：

package com.mybatis.inter;

import com.mybatis.bean.Customer;

public interface ICustomerDAO {

	public Customer selectCustomer(int id);

}

　　订单mapper接口定义：

package com.mybatis.inter;

import com.mybatis.bean.Order;

public interface IOrderDAO {

	public Order selectOrder(int id);
}

　　测试：

package com.mybatis.test;

import java.io.IOException;

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;

import com.mybatis.bean.Customer;
import com.mybatis.bean.Order;
import com.mybatis.inter.ICustomerDAO;
import com.mybatis.inter.IOrderDAO;
import com.mybatis.util.MybatisUtil;

public class Test {
	public static void main(String[] args) {
		SqlSessionFactory factory = null;
		SqlSession session=null;
		try {
			factory=MybatisUtil.getSqlSessionFactory();
			session=factory.openSession();
			ICustomerDAO customerDAO = session.getMapper(ICustomerDAO.class);
			Customer customer = customerDAO.selectCustomer(2);
			System.err.println(customer.getName()+" 买了：");
			for(Order order :customer.getOrderList()){
				System.err.println(order.getName() +" "+order.getPrice());
			}
			System.err.println("=========================================");
			IOrderDAO orderDAO = session.getMapper(IOrderDAO.class);
			Order order = orderDAO.selectOrder(2);
			System.err.println(order.getName()+" "+order.getPrice());
			System.err.println(order.getCustomer().getName());
		} catch (IOException e) {
			e.printStackTrace();
		}finally{
			if(session != null)
				session.close();
		}

	}
}