通过

$facet

$facet 阶段聚合管道允许在单个管道阶段内执行多个并行聚合。 其可用于在单个查询中对同一数据集执行多个分析。

语法

$facet 阶段的语法如下所示：

{
  "$facet": {
    "outputField1": [ { "stage1": {} }, { "stage2": {} } ],
    "outputField2": [ { "stage1": {} }, { "stage2": {} } ]
  }
}

参数

参数 说明
outputFieldN 输出字段的名称。
stageN 要执行的聚合阶段。

例子

请考虑商店集合中的这个示例文档。

{
    "_id": "0fcc0bf0-ed18-4ab8-b558-9848e18058f4",
    "name": "First Up Consultants | Beverage Shop - Satterfieldmouth",
    "location": {
        "lat": -89.2384,
        "lon": -46.4012
    },
    "staff": {
        "totalStaff": {
            "fullTime": 8,
            "partTime": 20
        }
    },
    "sales": {
        "totalSales": 75670,
        "salesByCategory": [
            {
                "categoryName": "Wine Accessories",
                "totalSales": 34440
            },
            {
                "categoryName": "Bitters",
                "totalSales": 39496
            },
            {
                "categoryName": "Rum",
                "totalSales": 1734
            }
        ]
    },
    "promotionEvents": [
        {
            "eventName": "Unbeatable Bargain Bash",
            "promotionalDates": {
                "startDate": {
                    "Year": 2024,
                    "Month": 6,
                    "Day": 23
                },
                "endDate": {
                    "Year": 2024,
                    "Month": 7,
                    "Day": 2
                }
            },
            "discounts": [
                {
                    "categoryName": "Whiskey",
                    "discountPercentage": 7
                },
                {
                    "categoryName": "Bitters",
                    "discountPercentage": 15
                },
                {
                    "categoryName": "Brandy",
                    "discountPercentage": 8
                },
                {
                    "categoryName": "Sports Drinks",
                    "discountPercentage": 22
                },
                {
                    "categoryName": "Vodka",
                    "discountPercentage": 19
                }
            ]
        },
        {
            "eventName": "Steal of a Deal Days",
            "promotionalDates": {
                "startDate": {
                    "Year": 2024,
                    "Month": 9,
                    "Day": 21
                },
                "endDate": {
                    "Year": 2024,
                    "Month": 9,
                    "Day": 29
                }
            },
            "discounts": [
                {
                    "categoryName": "Organic Wine",
                    "discountPercentage": 19
                },
                {
                    "categoryName": "White Wine",
                    "discountPercentage": 20
                },
                {
                    "categoryName": "Sparkling Wine",
                    "discountPercentage": 19
                },
                {
                    "categoryName": "Whiskey",
                    "discountPercentage": 17
                },
                {
                    "categoryName": "Vodka",
                    "discountPercentage": 23
                }
            ]
        }
    ]
}

示例 1：针对销售和促销的分面搜索

针对指定的产品类别对销售和促销执行同时分析。 salesAnalysis 管道展开 salesByCategory，筛选特定类别，并将其分组以求和 totalSales。 促销分析管道展开促销事件及其折扣，筛选特定类别（如 Laptops、Smartphones 等），并将其分组以计算平均折扣百分比。 stores 集合中的输入文档仅在此操作开始时从数据库提取一次。

db.stores.aggregate([
  {
    $facet: {
      salesAnalysis: [
        { $unwind: "$sales.salesByCategory" },
        { $match: { "sales.salesByCategory.categoryName": { $in: ["Laptops", "Smartphones", "Cameras", "Watches"] } } },
        { $group: { _id: "$sales.salesByCategory.categoryName", totalSales: { $sum: "$sales.salesByCategory.totalSales" } } }
      ],
      promotionAnalysis: [
        { $unwind: "$promotionEvents" },
        { $unwind: "$promotionEvents.discounts" },
        { $match: { "promotionEvents.discounts.categoryName": { $in: ["Laptops", "Smartphones", "Cameras", "Watches"] } } },
        { $group: { _id: "$promotionEvents.discounts.categoryName", avgDiscount: { $avg: "$promotionEvents.discounts.discountPercentage" } } }
      ]
    }
  }
]).pretty();

查询返回的输出显示已聚合的见解。

{
  "salesAnalysis": [
    { "_id": "Smartphones", "totalSales": 440815 },
    { "_id": "Laptops", "totalSales": 679453 },
    { "_id": "Cameras", "totalSales": 481171 },
    { "_id": "Watches", "totalSales": 492299 }
  ],
  "promotionAnalysis": [
    { "_id": "Smartphones", "avgDiscount": 14.32 },
    { "_id": "Laptops", "avgDiscount": 14.780645161290323 },
    { "_id": "Cameras", "avgDiscount": 15.512195121951219 },
    { "_id": "Watches", "avgDiscount": 15.174418604651162 }
  ]
}

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