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  • 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();
    		}
    
    	}
    }
    

      

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  • 原文地址:https://www.cnblogs.com/zcs201093189/p/4844787.html
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