$[identifier] (as Array Update Operator)

  • Article
  • 05/23/2025

The $[identifier] array update operator in Azure Cosmos DB for MongoDB vCore is used to update specific elements in an array that match a given condition. This operator is particularly useful when you need to update multiple elements within an array based on certain criteria. It allows for more granular updates within documents, making it a powerful tool for managing complex data structures.

javascript

{
  "<update operator>": {
    "<array field>.$[<identifier>]": <value>
  }
},
{
  "arrayFilters": [
    { "<identifier>.<field>": <condition> }
  ]
}

Parameters

Parameter Description
<update operator> The update operator to be applied (e.g., $set, $inc, etc.).
<array field> The field containing the array to be updated.
<identifier> A placeholder used in arrayFilters to match specific elements in the array.
<value> The value to be set or updated.
arrayFilters An array of filter conditions to identify which elements to update.
<field> The specific field within array elements to be checked.
<condition> The condition that array elements must meet to be updated.

Example(s)

Example 1: Updating Discount Percentage for a Specific Category

Suppose you want to update the discount percentage for the "Laptops" category in the "Holiday Specials" promotion event.

db.collection.update(
  { "store.storeId": "12345", "store.promotionEvents.eventName": "Holiday Specials" },
  {
    $set: {
      "store.promotionEvents.$[event].discounts.$[discount].discountPercentage": 18
    }
  },
  {
    arrayFilters: [
      { "event.eventName": "Holiday Specials" },
      { "discount.categoryName": "Laptops" }
    ]
  }
)

Example 2: Increasing Total Sales by Category

Suppose you want to increase the total sales for the "Smartphones" category by $10,000.

db.collection.update(
  { "store.storeId": "12345" },
  {
    $inc: {
      "store.sales.salesByCategory.$[category].totalSales": 10000
    }
  },
  {
    arrayFilters: [
      { "category.categoryName": "Smartphones" }
    ]
  }
)

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