Question

在find的猫鼬查询（“ -_id services.location”）上，字符串化的输出为：

mInterstitialAd = new InterstitialAd(this);
        /*mInterstitialAd.setAdUnitId("ca-app-pub-3940256099942544/1033173712");
        mInterstitialAd.loadAd(new AdRequest.Builder().build());*/
        mInterstitialAd.setAdUnitId(String.valueOf(R.string.admob_interstitial_ad_id));
        mInterstitialAd.loadAd(new AdRequest.Builder().build());
        //.addTestDevice("25E662D1EDF4290XXXXXXXXXXXX")
        mInterstitialAd.setAdListener(new AdListener() {
            @Override
            public void onAdFailedToLoad(int i) {
                super.onAdFailedToLoad(i);
                Log.e("TAG", "ADMOB INTERSTITIAL AD - " + i);
            }

            public void onAdLoaded() {
                if (mInterstitialAd.isLoaded()) {
                    mInterstitialAd.show();
                } else {
                    Log.d("TAG", "The interstitial wasn't loaded yet.");
                }
            }
        });

有什么办法可以从我得到的输出中访问位置的每个单独值，例如（17.4374614，78.7482878,17.4020637 ....）

我的架构如下：-

[
   {
      "services":[
         {
            "location":[
               17.4374614,
               78.7482878
            ]
         },
         {
            "location":[
               17.4020637,
               78.18400519324596
            ]
         },
         {
            "location":[
               17.56208737,
               78.284005186526
            ]
         },
         {
            "location":[
               17.5620637,
               78.3240051999554
            ]
         }
      ]
   }
]

Answer 1

您正在寻找的是$reduce和$concatArrays运算符。

[
  {
    "$project": {
      "result": {
        "$reduce": {
          "input": "$services.location",
          "initialValue": [],
          "in": {
            "$concatArrays": [
              "$$this",
              "$$value"
            ]
          }
        }
      }
    }
  }
]

See demo

Answer 2

更新了以下答案：

有什么方法可以只渲染不带_id的loc值数组进入模板。我只需要渲染loc数组的值

您可以通过以下方法进行操作：https://mongoplayground.net/p/VhrZKxg6OC1

db.collection.aggregate([
  {
    $unwind: "$services"
  },
  {
    $unwind: "$services.location"
  },
  {
    $project: {
      "_id": "$_id",
      "location": "$services.location"
    }
  },
  {
    $group: {
      _id: "_id",
      loc: {
        $push: "$location"
      }
    }
  },
  {
    $project: {
      "_id": 0,
      "locationArray": "$loc"
    }
  }
])

这将导致：

[
  {
    "locationArray": [
      17.4374614,
      78.7482878,
      17.4020637,
      78.18400519324597,
      17.56208737,
      78.284005186526,
      17.5620637,
      78.3240051999554
    ]
  }
]

希望它可以解决您的查询。

从猫鼬find（）查询中提取一个值

2 个答案: