Mapper.xml中association和collection的区别

Mapper.xml中association和collection的区别：

• association 一对一或多对一
• collection 一对多

Mapper.xml文件中association的使用举例：

<resultMap type="Blog" id="BlogResult">
    <result property="id" column="id"/>
    <result property="title" column="title"/>
    <result property="summary" column="summary"/>
    <result property="releaseDate" column="releaseDate"/>
    <result property="clickHit" column="clickHit"/>
    <result property="replyHit" column="replyHit"/>
    <result property="content" column="content"/>
    <result property="keyWord" column="keyWord"/>
    <!-- 一对一 -->
    <association property="blogType" column="typeId" select="com.blog.dao.BlogTypeDao.selectBlogTypeById"/>
</resultMap>

Mapper.xml文件中collection的两种使用举例：

1. 直接指定该集合中元素的映射

   <resultMap type="User" id="userMap">
       <id property="id" column="uid"/>
       <result property="username" column="username"/>
       <result property="password" column="password"/>
       <!-- 一对多 -->
       <collection property="roles" ofType="Role">
           <id property="id" column="rid"/>
           <result property="name" column="rname"/>
           <!-- 一对多 -->
           <collection property="permissions" ofType="Permissions">
               <id property="id" column="pid"/>
               <result property="name" column="pname"/>
           </collection>
       </collection>
   </resultMap>
   

2. 引用别的Mapper.xml的查询方法

   <resultMap id="BaseResultMap" type="SysUser" >
       <id column="user_id" property="id" jdbcType="BIGINT" />
       <result column="username" property="username" jdbcType="VARCHAR" />
       <result column="password" property="password" jdbcType="VARCHAR" />
       <collection property="sysRoles" column="user_id"
                   select="com.space.sbsecurity.mapper.sys.SysRoleMapper.selectRoleListByUserId">
       </collection>
   </resultMap>