MyBatis中＜collection＞标签的多种用法

<!-- 主表的resultMap -->
<resultMap id="UserMap" type="User">
    <id property="id" column="id"/>
    <result property="username" column="username"/>
    <!-- 集合属性：permissions -->
    <collection 
        property="permissions" 
        ofType="Permission" 
        select="com.example.mapper.PermissionMapper.selectByUserId" 
        column="id"
    />
</resultMap>

<!-- 主表的查询SQL -->
<select id="selectUser" resultMap="UserMap">
    SELECT id, username FROM users WHERE id = #{id}
</select>

<!-- 子查询（PermissionMapper.xml） -->
<select id="selectByUserId" resultType="Permission">
    SELECT * FROM permissions WHERE user_id = #{id}
</select>

<!-- 主表的resultMap -->
<resultMap id="UserMap" type="User">
    <id property="id" column="user_id"/>
    <result property="username" column="username"/>
    <!-- 集合属性：orders -->
    <collection 
        property="orders" 
        ofType="Order" 
        columnPrefix="order_"
    >
        <id property="orderId" column="order_id"/>
        <result property="amount" column="amount"/>
    </collection>
</resultMap>

<!-- 主表的查询SQL（使用JOIN） -->
<select id="selectUserWithOrders" resultMap="UserMap">
    SELECT 
        u.id AS user_id, 
        u.username, 
        o.id AS order_id, 
        o.amount 
    FROM users u 
    LEFT JOIN orders o ON u.id = o.user_id 
    WHERE u.id = #{id}
</select>

<!-- 处理树形结构的resultMap -->
<resultMap id="CategoryMap" type="Category">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="parentId" column="parent_id"/>
    <!-- 递归查询子节点 -->
    <collection 
        property="children" 
        ofType="Category" 
        select="selectCategoriesByParentId" 
        column="id"
    />
</resultMap>

<!-- 查询父节点的子节点 -->
<select id="selectCategoriesByParentId" resultMap="CategoryMap">
    SELECT * FROM categories WHERE parent_id = #{id}
</select>

column="{param1=column1, param2=column2}"

<collection 
    property="items" 
    ofType="Item" 
    select="com.example.mapper.ItemMapper.selectItemsByUserAndDate" 
    column="{userId=id, date=createTime}"
/>

<!-- 显式指定javaType -->
<collection 
    property="permissions" 
    javaType="ArrayList" 
    ofType="Permission" 
    select="..." 
    column="..."
/>