$set

The $set operator updates an existing field or creates a new field with the specified value if it does not exist. One or more fields listed are updated or created. The dot notation is used to update or create nested objects.

{
  "$set": {
    "newField": <expression>,
    ...
  }
}

Consider this sample document from the stores collection in the StoreData database.

{
    "_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
                }
            ]
        }
    ]
}

db.stores.updateOne({"_id": "8eefe8bd-5d6f-4038-90e8-05a8277637f0"}, {"$set": {"name": "Lakeshore Retail"}})

db.stores.updateOne({"_id": "8eefe8bd-5d6f-4038-90e8-05a8277637f0"}, {"$set": {"staff.totalStaff.partTime": 9}})

Create a new field called "formerName" with the old name of the store.

db.stores.updateOne({"_id": "8eefe8bd-5d6f-4038-90e8-05a8277637f0"}, {"$set": {"formerName": "Tailwind Traders | Drone Shoppe - New Theodora"}})

Create a new field within the nested totalStaff object to specify a count of temporary staff members.

db.stores.updateOne({"_id": "8eefe8bd-5d6f-4038-90e8-05a8277637f0"}, {"$set": {"staff.totalStaff.temporary": 3}})

db.stores.updateOne({"_id": "8eefe8bd-5d6f-4038-90e8-05a8277637f0"}, {"$set": {"staff.totalStaff.partTime": 9, "sales.totalSales": 3611}})

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