MongoDb MapReduce按鍵非值分組

Question

我正在嘗試編寫一個mapreduce函數以從mongodb累積統計信息。 但是，創建數據結構的隊友將數據保存如下：

"statistics": {
    "20111206": {
      "CN": {
        "Beijing": {
          "cart": 1,
          "cart_users": [
            { "$oid" : "4EDD73938EAD0E5420000000" }
          ],
          "downloads": {
            "wmv": {
              "mid": 1
            }
          },
          "orders": {
            "wmv": {
              "mid": 1
            }
          }
        }
      }
    }
}

問題在於，我需要分組的許多值僅存儲在鍵中（例如示例中的CN或BEJING）。 這些可以是國家代碼，視頻格式等...所以我不想在mapreduce函數中對其中的任何一個進行編碼。

我用於化簡部分的forEach函數僅將值作為參數傳遞。

所以問題是：有沒有辦法在此上執行mapReduce並按鍵分組，或者我必須首先將數據轉換成看起來或多或少像這樣的新結構：

{
  "movie_id": "4edcd4f29a4e61c00c000059",
  "country": "CN",
  "city": "Beijing",
  "list": [
    {
      "user_id": { "$oid" : "4EDD75388EAD0E5720010000" },
      "downloads": {
        "cnt": 1,
        "list": [
          {
            "format": "wmv",
            "quality": "high"
          }
        ]
      },
      "orders": {
        "cnt": 1,
        "list": [
          {
            "format": "wmv",
            "quality": "high"
          }
        ]
      }
    }
  ]
}

Answer 1

假設您的收藏夾設置了如下記錄：

> db.test_col.findOne()
{
    "_id" : ObjectId("4f90ed994d2246dd7996e042"),
    "statistics" : {
        "20111206" : {
            "CN" : {
                "Beijing" : {
                    "cart" : 1,
                    "cart_users" : [
                        {
                            "oid" : "4EDD73938EAD0E5420000000"
                        }
                    ],
                    "downloads" : {
                        "wmv" : {
                            "mid" : 1
                        }
                    },
                    "orders" : {
                        "wmv" : {
                            "mid" : 1
                        }
                    }
                }
            }
        }
    }
}

這是一個將按國家/地區分組，提供城市列表以及該國家/地區總數的命令。 它應該讓你更接近你 正在 試圖做的事：

db.runCommand({ mapreduce: "test_col",
                map: function () {
                    var l0      = this.statistics,
                        date    = Object.keySet(l0)[0],
                        l1      = l0[date],
                        country = Object.keySet(l1)[0],
                        l2      = l1[country],
                        city    = Object.keySet(l2)[0],
                        data      = l2[city];
                    emit(country, { date: date, city: city, data: data });
                },
                reduce: function (country, values) {
                    var r = { cities: [], count: 0 };
                    values.forEach(function (v) {
                        if (r.cities.indexOf(v.city) == -1)         r.cities.push(v.city);
                        r.count++;
                    });
                    return r;
                },
                out: { reduce: "test_col_reduce" }
});

我的測試數據的輸出如下所示：

> db.test_col_reduce.find()
{ "_id" : "AR", "value" : { "cities" : [ "San Juan", "Buenos Aires", "Cordoba", "Rosario" ], "count" : 18 } }
{ "_id" : "BZ", "value" : { "cities" : [ "Morico", "San Ignacio", "Corozal" ], "count" : 15 } }
{ "_id" : "CN", "value" : { "cities" : [ "Beijing", "Shanghai", "HongKong" ], "count" : 26 } }
{ "_id" : "US", "value" : { "cities" : [ "San Diego", "Los Angeles", "San Francisco", "New York" ], "count" : 27 } }