mybatis高级映射（一对一，一对多）

mybatis高级映射

一对一关联映射

需求：查询订单信息，关联查询用户信息（一个订单对应一个用户）

（1）通过resultType实现

sql语句：

select
orders.* ,
USER.username,
USER. sex  ,
USER.address 
FROM orders , USER 
WHERE orders.userid = USER .id

创建pojo类

由于orders.java不能全部映射字段，所以要新建pojo

创建一个pojo继承包括查询字段较多的·一个po类

OrdersCustom.java (订单扩展类)

//订单扩展类
public class OrdersCustom extends Orders{
	//添加用户属性
	private String username;
	private String sex;
	private String address;
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	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;
	}
		
}

mapper.xml文件

<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="cn.mapper.OrdersMapperCustom">
	<select id="findOrdersUser" parameterType="" resultType="cn.po.OrdersCustom">
		select
		orders.* ,
		USER.username,
		USER. sex  ,
		USER.address 
		FROM orders , USER 
		WHERE orders.userid = USER .id
	</select>
</mapper>

（2）resultMap实现

sql语句

select
orders.* ,
USER.username,
USER. sex  ,
USER.address 
FROM orders , USER 
WHERE orders.userid = USER .id    

　在orders类中添加user

//用户信息
private User user;

生成get ，set 方法

mapper.xml

	<!-- 定义订单查询关联用户resultMap 
	将整合查询结果映射到cn.po.Orders-->
	<resultMap type="cn.po.Orders" id="OrdersUserResultMap">
		<!-- 映射订单信息，非关联  -->
		<!-- id唯一标识，如果有多个配置多个id -->
		<id column="id" property="id"></id>
		<result column=user_id" property="userid"></result>
		<result column=number" property="number"></result>
		<result column=createtime" property="createtime"></result>
		<result column="note" property="note"></result>
		<!-- 配置映射的关联用户信息 -->
		<!-- association用于映射关联查询单个对象的信息
			property 要将关联查询的用户信息映射到Orders的那个属性
		 -->
		<association property="user" javaType="cn.po.User">
			<!-- id关联用户的唯一标识
				colimn 指定唯一标识用户列
				javaType映射到user的那个属性
			 -->
			<id column="user_id" property="id"/>
			<result column="username" property="username"/>
			<result column="sex" property="sex"/>
			<result column="address" property="address"/>
		</association>
	</resultMap>
	<select id="findOrdersUser" parameterType="" resultMap="OrdersUserResultMap">
		select
		orders.* ,
		USER.username,
		USER. sex  ,
		USER.address 
		FROM orders , USER 
		WHERE orders.userid = USER .id
	</select>

一对多关联映射

需求：查询订单及订单明细（一个订单里有多个商品明细）

sql语句

select
orders.* ,
orderdetail.id orderdetail_id,
orderdetail.items_id,
orderdetail.items_num,
orderdetail.orders_id
FROM orders ,orderdetail 
WHERE orderdetail.orders_id = orders.id

在Orders类中添加订单明细（orderdetail.java）的list集合

//订单明细
private List<Orderdetail> orderdetail;

 mapper.xml

<resultMap type="cn.po.Orders" id="OrdersOrderdetailResultMap">
		<!-- 映射订单信息，非关联  -->
		<!-- id唯一标识，如果有多个配置多个id -->
		<id column="id" property="id"></id>
		<result column=user_id" property="userid"></result>
		<result column=number" property="number"></result>
		<result column=createtime" property="createtime"></result>
		<result column="note" property="note"></result>
		<!-- 配置映射的关联用户信息 -->
		<!-- collection用于映射关联查询多个记录映射到集合当中
			property 要将关联查询的用户信息映射到Orders的那个属性
		    ofType指定映射到集合属性中类型
		 -->
		 <collection property="orderdetail" ofType="cn.po.Orderdetail">
		 	<id column="orderdetail_id" property="id"></id>
		 	<result column="items_id" property="itemsid"></result>
		 	<result column="items_num" property="itemsnum"></result>
		 	<result column="orders_id" property="ordersid"></result>
		 </collection>
	</resultMap>
	<select id="findOrdersUser" parameterType="" resultMap="OrdersOrderdetailResultMap">
		select
		orders.* ,
		orderdetail.id orderdetail_id,
		orderdetail.items_id,
		orderdetail.items_num,
		orderdetail.orders_id
		FROM orders ,orderdetail 
		WHERE orderdetail.orders_id = orders.id
	</select>