Mybatis多表关联查询之多对一和一对多

周sir | 2017年6月15日 | mytatis | 0 条评论 | 4551

Mybatis多表关联可分成四种情况:一对一, 一对多, 多对一, 多对多.实现映射的关键是resultMap网上有很多介绍可自行搜索学习，如:MyBatis学习之二、SQL语句映射文件(1)resultMap

首先看下多对一实现

准备两张表person和order为1:n关系

类结构：

class7

映射文件:OrderMapper.xml

第一种映射方式:

<mapper namespace="com.ittx.mybatis.demo1.dao.OrderDao">
	<resultMap type="com.ittx.mybatis.demo1.model.Order" id="orderBean">
		<id column="orderId" property="id"/>
		<result column="orderNumber" property="number"/>
		<result column="orderPrice" property="price"/>
		<!-- 多对一的关系 -->
		<!--column:指外键值， property: 指的是属性的值, javaType：指的是属性的类型-->
		<association column="pid" property="person" javaType="com.ittx.mybatis.demo1.model.Person">
			<id column="personId" property="id"/>
			<result column="personName" property="name"/>
			<result column="personAddress" property="address"/>
			<result column="personTel" property="tel"/>
		</association>
	</resultMap>

	<!-- 根据id查询Order, 关联将Person查询出来 -->
	<select id="selectOrderById" parameterType="string" resultMap="orderBean">
		select p.*, o.* from person p, orders o where p.personId  = o.pid and o.orderId = #{id}
	</select>
</mapper>

第二种映射方式：

<mapper namespace="com.ittx.mybatis.demo1.dao.OrderDao">
	<resultMap type="com.ittx.mybatis.demo1.model.Person" id="personBaseBean">
		<id column="personId" property="id"/>
		<result column="personName" property="name"/>
		<result column="personAddress" property="address"/>
		<result column="personTel" property="tel"/>
	</resultMap>

	<resultMap type="com.ittx.mybatis.demo1.model.Order" id="orderBean">
		<id column="orderId" property="id"/>
		<result column="orderNumber" property="number"/>
		<result column="orderPrice" property="price"/>
		<!-- 多对一的关系 -->
		<!--column:指外键值， property: 指的是属性的值, resultMap：指的是属性的映射, -->
		<association column="pid" property="person" resultMap="com.ittx.mybatis.demo1.dao.OrderDao.personBaseBean"/>
	</resultMap>

	<!-- 根据id查询Order, 关联将Person查询出来 -->
	<select id="selectOrderById" parameterType="string" resultMap="orderBean">
		select p.*, o.* from person p, orders o where p.personId  = o.pid and o.orderId = #{id}
	</select>
</mapper>

第三种映射方式:

<mapper namespace="com.ittx.mybatis.demo1.dao.OrderDao">
<resultMap type="com.ittx.mybatis.demo1.model.Order" id="orderBean">
		<id column="orderId" property="id"/>
		<result column="orderNumber" property="number"/>
		<result column="orderPrice" property="price"/>
		<!-- 多对一的关系 -->
		<!--column:指外键值， property: 指的是属性的值, select:使用另一个查询封装的结果 -->
		<association column="orderId" property="person" select="selectPersonByOrderId"/>
	</resultMap>

	<select id="selectOrderById" parameterType="string"  resultMap="orderBean">
		select * from orders where orderId = #{id}
	</select>

	<select id="selectPersonByOrderId" parameterType="string" resultMap="com.ittx.mybatis.demo1.dao.OrderDao.personBaseBean">
		select * from person where personId in (select pid from orders where orderId = #{id})
	</select>
</mapper>

接着看一对多关联实现

表结构不变
类结构如下:

映射文件:PersonMapper.xml

第一种方式

<resultMap type="com.ittx.mybatis.demo1.model.Person" id="personBean">
		<id column="personId" property="id"/>
		<result column="personName" property="name"/>
		<result column="personAddress" property="address"/>
		<result column="personTel" property="tel"/>

		<!-- 一对多的关系 -->
		<!-- property: 指的是集合属性的值, ofType：指的是集合中元素的类型 -->
		<collection property="orders" ofType="com.ittx.mybatis.demo1.model.Order">
			<id column="orderId" property="id"/>
			<result column="orderNumber" property="number"/>
			<result column="orderPrice" property="price"/>
		</collection>
	</resultMap>

	<!-- 根据id查询Person, 关联将Orders查询出来 -->
	<select id="selectPersonById" parameterType="string" resultMap="personBean">
		select p.*, o.* from person p, orders o where p.personId  = o.pid and p.personId = #{id}
	</select>

第二种方式

<resultMap type="com.ittx.mybatis.demo1.model.Order" id="orderBaseBean">
		<id column="orderId" property="id"/>
		<result column="orderNumber" property="number"/>
		<result column="orderPrice" property="price"/>
	</resultMap>
	<resultMap type="com.ittx.mybatis.demo1.model.Person" id="personBean">
		<id column="personId" property="id"/>
		<result column="personName" property="name"/>
		<result column="personAddress" property="address"/>
		<result column="personTel" property="tel"/>

		<!-- 一对多的关系 -->
		<collection property="orders" resultMap="com.ittx.mybatis.demo1.dao.OrderDao.orderBaseBean"/>
	</resultMap>

	<!-- 根据id查询Person, 关联将Orders查询出来 -->
	<select id="selectPersonById" parameterType="string" resultMap="personBean">
		select p.*, o.* from person p, orders o where p.personId  = o.pid and p.personId = #{id}
	</select>