mybatis association的使用
在上一篇文章中介绍了collection的使用以及java bean,表的结构,今天进行association使用的学习,在多对一的映射关系中,查询到多的一方顺带查询出一的一方是常见的!在此例子中,在查询文章的时候顺带将作者查询出来!
映射文件为:
<?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="article">
<resultMap id="myMap" type="article">
<association column="user" property="user" javaType="user"
select="selectUser">
</association>
</resultMap>
<select id="selectUser" resultType="user">
select * from user
where id=#{id}
</select>
<sql id="article_saveWithUser">
insert into article(name,time,user)
values(#{name},#{time},#{user.id})
</sql>
<sql id="article_saveNoUser">
insert into article(name,time) values(#{name},#{time})
</sql>
<select id="article_selectAll" resultMap="myMap">
select * from
article
</select>
<insert id="article_save" parameterType="article">
<if test="user!=null">
<include refid="article_saveWithUser" />
</if>
<if test="user==null">
<include refid="article_saveNoUser" />
</if>
</insert>
</mapper>
测试:
@Test
public void testSelectAll()
{
List<Article> result = service.findAll(null);
for (Article a : result)
{
System.out.println(a);
}
}
结果:
Article [id=1, name=firstArticle, time=2013-11-3 0:00:00, user=User [article=null, id=1, name=d]]
Article [id=2, name=secondArticle, time=2013-11-3 0:00:00, user=User [article=null, id=1, name=d]]
级联查询成功!