$pop (array update)

The $pop operator in MongoDB is used to remove the first or last element of an array. This operator is useful when you need to manage arrays by removing elements from either end. The $pop operator can be used in update operations.

{ $pop: { <field>: <value> } }

• <field>: The field that contains the array from which you want to remove an element.
• <value>: Use 1 to remove the last element, and -1 to remove the first element.

Let's understand the usage with the following sample json.

{
  "_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5",
   "name": "Lakeshore Retail | DJ Equipment Stop - Port Cecile",
  "location": {
    "lat": 60.1441,
    "lon": -141.5012
  },
  "staff": {
    "totalStaff": {
      "fullTime": 2,
      "partTime": 0
    }
  },
  "sales": {
    "salesByCategory": [
      {
        "categoryName": "DJ Headphones",
        "totalSales": 35921
      }
    ],
    "fullSales": 3700
  },
  "promotionEvents": [
    {
      "eventName": "Bargain Blitz Days",
      "promotionalDates": {
        "startDate": {
          "Year": 2024,
          "Month": 3,
          "Day": 11
        },
        "endDate": {
          "Year": 2024,
          "Month": 2,
          "Day": 18
        }
      },
      "discounts": [
        {
          "categoryName": "DJ Turntables",
          "discountPercentage": 18
        },
        {
          "categoryName": "DJ Mixers",
          "discountPercentage": 15
        }
      ]
    }
  ],
  "tag": [
    "#ShopLocal",
    "#SeasonalSale",
    "#FreeShipping",
    "#MembershipDeals"
  ]
}

db.stores.update(
  { "_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5" },
  { $pop: { "tag": 1 } }
)

This query would return the following document. The last element from the array is removed.

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

db.stores.update(
  { "_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5" },
  { $pop: { "promotionEvents": -1 } }
)

This query would return the following document. The first element from the array is removed.

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

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