Mybatis高級-resultMap之collection聚集

簡介
聚集元素用來處理“一對多”的關係。需要指定映射的Java實體類的屬性，屬性的javaType（一般爲ArrayList）；列表中對象的類型ofType（Java實體類）；對應的數據庫表的列名稱；
額，估計這樣說大家聽不懂，簡單的意思就是把兩張表聯繫起來，用於解決一些奇怪的需求
代碼
1.定義簡單的sql片段

<!-- 基本查詢-->
    <sql id="vo_select">
        SELECT
            vo.expenseId,
            vo.projectId,
            vo.expenseUserId,
            sua.realName as expenseUserName,
            vo.expenseTime,
            vo.expenseTypeId,
            vo.beneficialDepartmentId,
            sd.name as beneficialDepartmentName,
            vo.currencyId,
            vo.money,
            vo.paperCheckerId,
            vo.paperCheckerTime,
            vo.paidDepartmentId,
            vo.paidUserId,
            vo.paidTime,
            vo.expenseNote,
            vo.description,
            vo.currentStatus,
            vo.invoiceAmount,
            vo.paperFlag,
            vo.recordFlag,
            vo.createUserId,
            vo.createTime
        FROM p_expense vo
        INNER JOIN sys_user_archive sua ON sua.userId=vo.expenseUserId
        INNER JOIN sys_department sd ON sd.departmentId=vo.beneficialDepartmentId
    </sql>

2.查詢條件拼接，返回resultMap

<select id="findAll" parameterType="Pasv" resultMap="pexpenseMap">
        <include refid="vo_select"/>
        WHERE 1=1
        <!--根據登陸人判斷流程審覈步驟的人是否一樣 -->
        <if test="vo.userId !=null and vo.userId !=''">
        AND
        (
         EXISTS(
             select 0 from p_expense_flow pef 
             where pef.flag=0 and pef.checkUserIds like concat('%#',#{vo.userId},'#%')
             AND pef.expenseID=vo.expenseId
         )
        )
        </if>

        <!-- 根據時間查詢 -->
        <if test="vo.searchStartTime !=null and vo.searchStartTime !=''">
            AND vo.createTime >=DATE_FORMAT(#{vo.searchStartTime},'%Y-%m-%d')
        </if>
        <if test="vo.searchEndTime !=null and vo.searchEndTime !=''">
            AND vo.createTime <DATE_FORMAT(date_add(#{vo.searchEndTime}, INTERVAL 1 day),'%Y-%m-%d')
        </if>
        <!-- 註釋掉是避免從我的任務中查詢顯示一條數據-->
        <!-- <if test="null!=vo.expenseId and ''!=vo.expenseId">
            AND vo.expenseId = #{vo.expenseId}
        </if> -->
        <if test="null!=vo.projectId and ''!=vo.projectId">
            AND vo.projectId = #{vo.projectId}
        </if>
        <if test="null!=vo.expenseUserId and ''!=vo.expenseUserId">
            AND vo.expenseUserId = #{vo.expenseUserId}
        </if>
        <if test="null!=vo.expenseTime and ''!=vo.expenseTime">
            AND vo.expenseTime = #{vo.expenseTime}
        </if>
        <if test="null!=vo.expenseTypeId and ''!=vo.expenseTypeId">
            AND vo.expenseTypeId = #{vo.expenseTypeId}
        </if>
        <if test="null!=vo.beneficialDepartmentId and ''!=vo.beneficialDepartmentId">
            AND vo.beneficialDepartmentId = #{vo.beneficialDepartmentId}
        </if>
        <if test="null!=vo.currencyId and ''!=vo.currencyId">
            AND vo.currencyId = #{vo.currencyId}
        </if>
        <if test="null!=vo.money and ''!=vo.money">
            AND vo.money = #{vo.money}
        </if>
        <!-- 根據報銷人 -->
        <if test="vo.searchName !=null and vo.searchName !=''">
            AND sua.realName LIKE CONCAT(CONCAT('%', #{vo.searchName}),'%')
        </if>
        <if test="null!=vo.paperCheckerId and ''!=vo.paperCheckerId">
            AND vo.paperCheckerId = #{vo.paperCheckerId}
        </if>
        <if test="null!=vo.paperCheckerTime and ''!=vo.paperCheckerTime">
            AND vo.paperCheckerTime = #{vo.paperCheckerTime}
        </if>
        <if test="null!=vo.paidDepartmentId and ''!=vo.paidDepartmentId">
            AND vo.paidDepartmentId = #{vo.paidDepartmentId}
        </if>
        <if test="null!=vo.paidUserId and ''!=vo.paidUserId">
            AND vo.paidUserId = #{vo.paidUserId}
        </if>
        <if test="null!=vo.paidTime and ''!=vo.paidTime">
            AND vo.paidTime = #{vo.paidTime}
        </if>
        <if test="null!=vo.description and ''!=vo.description">
            AND vo.description = #{vo.description}
        </if>
        <if test="null!=vo.currentStatus and ''!=vo.currentStatus">
            AND vo.currentStatus = #{vo.currentStatus}
        </if>
        <if test="null!=vo.invoiceAmount and ''!=vo.invoiceAmount">
            AND vo.invoiceAmount = #{vo.invoiceAmount}
        </if>
        <if test="null!=vo.paperFlag and ''!=vo.paperFlag">
            AND vo.paperFlag = #{vo.paperFlag}
        </if>
        <if test="null!=vo.recordFlag and ''!=vo.recordFlag">
            AND vo.recordFlag = #{vo.recordFlag}
        </if>
        <if test="null!=vo.createUserId and ''!=vo.createUserId">
            AND vo.createUserId = #{vo.createUserId}
        </if>
        <if test="null!=vo.createTime and ''!=vo.createTime">
            AND vo.createTime = #{vo.createTime}
        </if>
        <if test="null!=vo.enabled and ''!=vo.enabled">
            AND vo.enabled = #{vo.enabled}
        </if>
        <!-- 根據報銷金額範圍查詢 -->
        <if test="vo.searchStartMoney !=null and vo.searchStartMoney !='' and vo.searchStartMoney!=0">
         and vo.money <![CDATA[ >= ]]> #{vo.searchStartMoney}
        </if>
        <if test="vo.searchEndMoney !=null and vo.searchEndMoney !='' and vo.searchEndMoney!=0">
         and vo.money <![CDATA[ <= ]]> #{vo.searchEndMoney}
        </if>
    </select>

3.定義resultMap，用於上面返回的resultMap，重點在於collection，先看代碼，我下面解釋

<resultMap type="com.account.web.vo.project.PExpenseVo" id="pexpenseMap">
        <id column="expenseId" property="expenseId"/>
        <result column="projectId" property="projectId"/>
        <result column="expenseUserId" property="expenseUserId"/>
        <result column="expenseUserName" property="expenseUserName"/>
        <result column="expenseTime" property="expenseTime"/>
        <result column="expenseTypeId" property="expenseTypeId"/>
        <result column="beneficialDepartmentId" property="beneficialDepartmentId"/>
        <result column="beneficialDepartmentName" property="beneficialDepartmentName"/>
        <result column="currencyId" property="currencyId"/>
        <result column="money" property="money"/>
        <result column="paperCheckerId" property="paperCheckerId"/>
        <result column="paperCheckerTime" property="paperCheckerTime"/>
        <result column="paidDepartmentId" property="paidDepartmentId"/>
        <result column="paidUserId" property="paidUserId"/>
        <result column="paidTime" property="paidTime"/>
        <result column="expenseNote" property="expenseNote"/>
        <result column="description" property="description"/>
        <result column="currentStatus" property="currentStatus"/>
        <result column="invoiceAmount" property="invoiceAmount"/>
        <result column="paperFlag" property="paperFlag"/>
        <result column="recordFlag" property="recordFlag"/>
        <result column="createUserId" property="createUserId"/>
        <result column="createTime" property="createTime"/>
        <collection property="checkers"  ofType="com.account.web.vo.admin.system.SysUserArchiveVo"
         select="findChecker3" column="{expenseId2=expenseId}">
        </collection>
    </resultMap>

4.定義collection用的sql片段

<select id="findChecker3" resultType="com.account.web.vo.admin.system.SysUserArchiveVo">
        select pef.expenseFlowId,sua.userId,sua.realName,pef.folwMomentId as folwMomentId
        from sys_user_archive sua
        INNER JOIN p_expense_flow pef ON pef.checkUserId =sua.userId 
        AND pef.expenseid=#{expenseId2}
    </select>

**低調小熊貓獨家解析
先給大家看一張圖，我就是靠這一張圖學會的，不要說圖看不清楚，自己ctrl+

ok，這樣聰明的估計就學會了，不會的看上面代碼吧
額，還是解釋幾個地方**

       <collection property="checkers" ofType="com.account.web.vo.admin.system.SysUserArchiveVo"
         select="findChecker3" column="{expenseId2=expenseId}">
        </collection>

**1.property=”checkers”就是上面那個resultMap返回的實體類裏面封裝的一個集合屬性。

2.ofType=”com.account.web.vo.admin.system.SysUserArchiveVo”就是集合的類型

3.select=”findChecker3”就是第四步使用的sql片段的id

4.column=”{expenseId2=expenseId}”那，這個就比較重要了，expenseId就是上面resultMap的字段的名字，expenseId2就是下面sql片段裏面條件接收值的字段**