<ruby id="bdb3f"></ruby>

    <p id="bdb3f"><cite id="bdb3f"></cite></p>

      <p id="bdb3f"><cite id="bdb3f"><th id="bdb3f"></th></cite></p><p id="bdb3f"></p>
        <p id="bdb3f"><cite id="bdb3f"></cite></p>

          <pre id="bdb3f"></pre>
          <pre id="bdb3f"><del id="bdb3f"><thead id="bdb3f"></thead></del></pre>

          <ruby id="bdb3f"><mark id="bdb3f"></mark></ruby><ruby id="bdb3f"></ruby>
          <pre id="bdb3f"><pre id="bdb3f"><mark id="bdb3f"></mark></pre></pre><output id="bdb3f"></output><p id="bdb3f"></p><p id="bdb3f"></p>

          <pre id="bdb3f"><del id="bdb3f"><progress id="bdb3f"></progress></del></pre>

                <ruby id="bdb3f"></ruby>

                ??碼云GVP開源項目 12k star Uniapp+ElementUI 功能強大 支持多語言、二開方便! 廣告
                ## $unwind * 將文檔中的某一個數組類型字段拆分成多條,每條包含數組中的一個值 ## 語法1 * 對某字段值進行拆分 ~~~ db.集合名稱.aggregate([{$unwind:'$字段名稱'}]) ~~~ * 構造數據 ~~~ db.t2.insert({_id:1,item:'t-shirt',size:['S','M','L']}) ~~~ * 查詢 ~~~ db.t2.aggregate([{$unwind:'$size'}]) ~~~ ## 語法2 * 對某字段值進行拆分 * 處理空數組、非數組、無字段、null情況 ~~~ db.inventory.aggregate([{ $unwind:{ path:'$字段名稱', preserveNullAndEmptyArrays:<boolean>#防止數據丟失 } }]) ~~~ * 構造數據 ~~~ db.t3.insert([ { "_id" : 1, "item" : "a", "size": [ "S", "M", "L"] }, { "_id" : 2, "item" : "b", "size" : [ ] }, { "_id" : 3, "item" : "c", "size": "M" }, { "_id" : 4, "item" : "d" }, { "_id" : 5, "item" : "e", "size" : null } ]) ~~~ * 使用語法1查詢 ~~~ db.t3.aggregate([{$unwind:'$size'}]) ~~~ * 查看查詢結果,發現對于空數組、無字段、null的文檔,都被丟棄了 * 問:如何能不丟棄呢? * 答:使用語法2查詢 ~~~ db.t3.aggregate([{$unwind:{path:'$sizes',preserveNullAndEmptyArrays:true}}]) ~~~
                  <ruby id="bdb3f"></ruby>

                  <p id="bdb3f"><cite id="bdb3f"></cite></p>

                    <p id="bdb3f"><cite id="bdb3f"><th id="bdb3f"></th></cite></p><p id="bdb3f"></p>
                      <p id="bdb3f"><cite id="bdb3f"></cite></p>

                        <pre id="bdb3f"></pre>
                        <pre id="bdb3f"><del id="bdb3f"><thead id="bdb3f"></thead></del></pre>

                        <ruby id="bdb3f"><mark id="bdb3f"></mark></ruby><ruby id="bdb3f"></ruby>
                        <pre id="bdb3f"><pre id="bdb3f"><mark id="bdb3f"></mark></pre></pre><output id="bdb3f"></output><p id="bdb3f"></p><p id="bdb3f"></p>

                        <pre id="bdb3f"><del id="bdb3f"><progress id="bdb3f"></progress></del></pre>

                              <ruby id="bdb3f"></ruby>

                              哎呀哎呀视频在线观看