mybatis多表关联

3、定义sql映射文件

（1）首先是一对多关联：

MyBatis中使用collection标签来解决一对一的关联查询，collection标签可用的属性如下：property:指的是集合属性的值ofType:指的是集合中元素的类型column:所对应的外键字段名称select:使用另一个查询封装的结果

<?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.mucfc.model.CustomerMapper">   <!-- 定义数据库字段与实体对象的映射关系 -->      <resultMap type="Customer" id="customerBean">          <id column="customerId" property="customerId"/>          <result column="customerName" property="customerName"/>          <result column="customerTel" property="customerTel"/>               <!-- 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="tickets" ofType="Ticket">              <id column="ticketId" property="ticketId"/>              <result column="ticketAddress" property="ticketAddress"/>              <result column="ticketPrice" property="ticketPrice"/>              <result column="ticketCId" property="ticketCId"/>          </collection>      </resultMap>               <!-- 根据id查询Person, 关联将Orders查询出来 -->      <select id="selectCustomerByName" parameterType="string" resultMap="customerBean">          select c.*,t.* from t_customer c,t_ticket t  where  c.customerId=t.ticketCId and c.customerName =#{customerName};      </select>          </mapper>

（2）接着是一对一关联：

 

MyBatis中使用association标签来解决一对一的关联查询，association标签可用的属性如下：property:对象属性的名称javaType:对象属性的类型column:所对应的外键字段名称select:使用另一个查询封装的结果

<?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.mucfc.model.TicketMapper">      <!-- 定义数据库字段与实体对象的映射关系  -->      <resultMap type="Ticket" id="ticketBean">          <id column="ticketId" property="ticketId" />          <result column="ticketAddress" property="ticketAddress" />          <result column="ticketPrice" property="ticketPrice" />          <result column="ticketCId" property="ticketCId" />          <!-- 一对一的关系 -->          <!-- property: 指的是属性的值, javaType：指的是元素的类型 -->          <association property="customer" javaType="Customer">              <id column="customerId" property="customerId" />              <result column="customerName" property="customerName" />              <result column="customerTel" property="customerTel" />          </association>      </resultMap>      <!-- 根据id查询ticket, 关联将Customer查询出来 -->      <select id="selectTicketById" parameterType="int" resultMap="ticketBean">          select c.*,t.* from t_customer c,t_ticket t where          c.customerId=t.ticketCId and t.ticketId =#{ticketId}      </select>  </mapper>

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