mybatis 多表关联映射

1、一对一
关键字：association
作用：针对pojo对象属性的映射
property：pojo的属性名
javaType：pojo类名
(1) 嵌套结果: 使用嵌套结果映射来处理重复的联合结果的子集

<resultMap type="com.gec.domain.Person" id="basePersonResultMap">
  	<id column="id" property="personId"/>
  	<result column="name" property="name"/>
  	<result column="sex" property="sex"/>
  	<result column="age" property="age"/>
	
  	<association property="card" javaType="com.gec.domain.Card">
  		<!-- 1、构造器注入
		<constructor>
  			<idArg column="id" javaType="int"/>
  			<arg column="code" javaType="string"/>
  		</constructor> 
		-->
		<!-- 2、setter注入 -->
  		<result column="id" property="cardId"/>
  		<result column="code" property="code"/>
  	</association>
 </resultMap>
  <select id="queryUserList" resultMap="basePersonResultMap">
  	select p.id as personId,p.name,p.sex,p.age,c.*
  	from tbl_person p,tbl_card c where p.card_id=c.id;
  </select>

2 、一对多
mybatis如何实现一对多的实现？(学生与班级)
(1) 嵌套结果:
ClazzMapper.xml


<resultMap type="com.gec.domain.Clazz" id="baseClazzResultMap">
	<id column="id" property="clazzId"/>
	<result column="clazz_name" property="clazzName"/>
	<result column="code" property="code"/>
</resultMap>
<resultMap type="com.gec.domain.Clazz" id="queryClazzList2ResultMap" extends="baseClazzResultMap">
	<collection property="studentList" javaType="ArrayList" ofType="com.gec.domain.Student">
		<id column="stu_id" property="studentId"/>
		<result column="name" property="name"/>
		<result column="sex" property="sex"/>
		<result column="age" property="age"/>
	</collection>
</resultMap>
<select id="queryClazzList2" resultMap="queryClazzList2ResultMap">
	SELECT c.*, s.id AS stu_id,s.name,s.sex,s.age
	FROM tbl_clazz c LEFT JOIN tbl_student s
	ON c.id=s.clazz_id;
</select>

3、多对多
商品表、订单表之间就是以多对多关联
商品与订单的关系表
描述多对多的数据表实现
(1)商品pojo:
Article.java


public class Article implements Serializable {
	private Integer articleId;
	private String name;
	private Double price;
	private String remark;
	private List<Order> orders;
	省略setter/gettera方法
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "mybatis-3-mapper.dtd" >
<mapper namespace="com.gec.mapper.ArticleMapper">
	<resultMap type="article" id="baseArticleResultMap">
		<id column="id" property="articleId"/>
		<result column="NAME" property="name"/>
		<result column="price" property="price"/>
		<result column="remark" property="remark"/>
	</resultMap>
	<resultMap type="article" id="findArtcleByIdResultMap" extends="baseArticleResultMap">
		<collection property="orders" javaType="ArrayList"
			ofType="com.gec.domain.Article" column="id"
			select="com.gec.mapper.OrderMapper.findOrderByArticleId"
		>
		</collection>
	</resultMap>
	<!-- 根据订单id查询商品 -->
	<select id="findArtcleByOrderId" resultMap="baseArticleResultMap">
		select * from tb_article  where id 
		in (select article_id from tb_item where order_id=#{id}) 
	</select>
	<select id="findArtcleById" resultMap="findArtcleByIdResultMap">
		select * from tb_article  where id=#{id}
	</select>
</mapper>

mybatis 多表关联映射

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