MyBatis 一对一

需求：实体是blog 和author 关系是一对一，查询 blog 以及 blog 的作者信息

• 嵌套查询：相当于是两次查询

<select id="selectBlogAuthor" resultMap="blogResultMap" parameterType="int">
    select * from blog  where bid = #{id, jdbcType=INTEGER}
</select>

<resultMap id="blogResultMap" type="com.chuang.resultmap.BlogResultMap">    
    <id column="bid" jdbcType="INTEGER" property="bid" />
    <result column="name" jdbcType="STRING" property="name" />
    <association property="author" colmn="author_id" 
                 select="com.chuang.dao.AuthorMapper.selectByPrimaryKey"/>  
<resultMap>

• 嵌套结果

<select id="selectBlogAuthor" resultMap="blogResultMap" parameterType="int">
    select * from blog b,author a
    where bid = #{id, jdbcType=INTEGER}
    and b.author_id = a.aid
</select>

<resultMap id="blogResultMap" type="com.chuang.resultmap.BlogResultMap">    
    <id column="bid" jdbcType="INTEGER" property="bid" />
    <result column="name" jdbcType="STRING" property="name" />
    <association property="author" javaType="com.chuang.Author">
        <!-- 映射 -->
        <id property="aid" column="aid" jdbcType="INTEGER"/>
        <result property="authorName" column="author_name" jdbcType="STRING"/>
    </association>  
<resultMap>