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$[]

The $[] all positional operator applies an update to every element of an array in each matched document. Unlike $, it doesn't depend on which element the query matched, and unlike $[<identifier>], it takes no arrayFilters. If the path holds a value that isn't an array, the update fails.

Syntax

db.collection.update(
   <query>,
   {
     $set: {
       <arrayField>.$[]: <value>
     }
   }
)

Parameters

Parameter	Description
`<query>`	The selection criteria for the documents to update.
`<arrayField>`	The field containing the array to update.
`<value>`	The value to set for each element in the array.

Examples

Consider this sample document from the stores collection.

{
    "_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
                }
            ]
        }
    ]
}

Example 1: Updating Discount Percentages

This query updates all elements in the discounts array inside each promotion event.

db.stores.updateOne(
  { _id: "0fcc0bf0-ed18-4ab8-b558-9848e18058f4" },
  {
    $inc: {
      "promotionEvents.$[].discounts.$[].discountPercentage": 5
    }
  }
)

Example 2: Updating Sales by Category

This query increase the total sales for all categories by 10% by using the $[] operator.

db.stores.update(
  { _id: "0fcc0bf0-ed18-4ab8-b558-9848e18058f4" },
  {
    $mul: {
      "sales.salesByCategory.$[].totalSales": 1.10
    }
  }
)