$addToSet (添加到集合)

$addToSet 运算符向数组中添加尚不存在的元素，同时确保集内元素的唯一性。

Syntax

{
  $addToSet: { <field1>: <value1> }
}

参数

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：向数组添加新标记tag

此查询将新标记添加到标记数组，使用 $addToSet 运算符运行查询以添加新值。

db.stores.updateOne({
    _id: "0fcc0bf0-ed18-4ab8-b558-9848e18058f4"
}, {
    $addToSet: {
        tag: "#ShopLocal"
    }
})

此查询返回以下结果：

[
  {
    "acknowledged": true,
    "insertedId": null,
    "matchedCount": "1",
    "modifiedCount": "0",
    "upsertedCount": 0
  }
]

示例 2：向 promotionEvents 数组添加新的促销事件

此查询将新事件添加到 promotionEvents 数组，使用$addToSet运算符和要添加的新提升对象运行查询。

db.stores.updateOne({
    _id: "0fcc0bf0-ed18-4ab8-b558-9848e18058f4"
}, {
    $addToSet: {
        promotionEvents: {
            eventName: "Summer Sale",
            promotionalDates: {
                startDate: {
                    Year: 2024,
                    Month: 6,
                    Day: 1
                },
                endDate: {
                    Year: 2024,
                    Month: 6,
                    Day: 15
                }
            },
            discounts: [{
                categoryName: "DJ Speakers",
                discountPercentage: 20
            }]
        }
    }
})

此查询返回以下结果：

[
  {
    "acknowledged": true,
    "insertedId": null,
    "matchedCount": "1",
    "modifiedCount": "1",
    "upsertedCount": 0
  }
]

示例 3 - 将$addToSet与$setWindowOperators配合使用

若要检索“First Up Consultants”公司内每家商店所在城市的列表，请运行一个先将商店按公司分区的查询。 然后，使用 $addToSet 运算符为分区中的每个商店添加不同的城市。

db.stores.aggregate([{
    $match: {
        company: {
            $in: ["First Up Consultants"]
        }
    }
}, {
    $setWindowFields: {
        partitionBy: "$company",
        sortBy: {
            "sales.totalSales": -1
        },
        output: {
            citiesForCompany: {
                $push: "$city",
                window: {
                    documents: ["unbounded", "current"]
                }
            }
        }
    }
}, {
    $project: {
        company: 1,
        name: 1,
        citiesForCompany: 1
    }
}])

此查询返回的前两个结果为：

[
    {
        "_id": "a1713bed-4c8b-46e7-bb68-259045dffdb4",
        "name": "First Up Consultants | Bed and Bath Collection - Jaskolskiside",
        "company": "First Up Consultants",
        "citiesForCompany": [
            "South Thelma",
            "South Carmenview",
            "Port Antone",
            "Charlotteville",
            "South Lenorafort",
            "Jaskolskiside"
        ]
    },
    {
        "_id": "6b8585ab-4357-4da7-8625-f6a1cd5796c5",
        "name": "First Up Consultants | Computer Depot - West Zack",
        "company": "First Up Consultants",
        "citiesForCompany": [
            "South Thelma",
            "South Carmenview",
            "Port Antone",
            "Charlotteville",
            "South Lenorafort",
            "Jaskolskiside",
            "West Zack"
        ]
    }
]

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