Edit

Share via

$exists (element query)

APPLIES TO: MongoDB vCore

The $exists operator matches documents that have the specified field. When $exists is true, it selects documents that contain the field, including documents where the field value is null. When $exists is false, the query returns only documents that do not contain the field.

Syntax

The syntax for the $exists operator is as follows:

{
  <field>: { $exists: <boolean> }
}

Parameters

Description
field The field to check for existence.
boolean true to match documents that contain the field (including null values), false to match documents that do not contain the field.

Example

Let's understand the usage with sample JSON from the stores dataset.

{
  "_id": "905d1939-e03a-413e-a9c4-221f74055aac",
  "name": "Trey Research | Home Office Depot - Lake Freeda",
  "location": { "lat": -48.9752, "lon": -141.6816 },
  "staff": { "employeeCount": { "fullTime": 12, "partTime": 19 } },
  "sales": {
    "salesByCategory": [ { "categoryName": "Desk Lamps", "totalSales": 37978 } ],
    "revenue": 37978
  },
  "promotionEvents": [
    {
      "eventName": "Crazy Deal Days",
      "promotionalDates": {
        "startDate": { "Year": 2023, "Month": 9, "Day": 27 },
        "endDate": { "Year": 2023, "Month": 10, "Day": 4 }
      },
      "discounts": [
        { "categoryName": "Desks", "discountPercentage": 22 },
        { "categoryName": "Filing Cabinets", "discountPercentage": 23 }
      ]
    }
  ],
  "company": "Trey Research",
  "city": "Lake Freeda",
  "storeOpeningDate": "2024-09-26T22:55:25.779Z",
  "lastUpdated": "Timestamp({ t: 1729983325, i: 1 })"
}

Example 1: Find stores with promotion events

The example finds all stores that have promotion events defined.

db.stores.find(
  { "promotionEvents": { $exists: true }},
  { "_id": 1, "promotionEvents": { $slice: 1 }}
).limit(2)

The query returns all documents where the promotionEvents field exists, regardless of whether the array is empty or contains elements.

  {
    "_id": "a715ab0f-4c6e-4e9d-a812-f2fab11ce0b6",
    "name": "Lakeshore Retail | Holiday Supply Hub - Marvinfort",
    "location": { "lat": -74.0427, "lon": 160.8154 },
    "staff": { "employeeCount": { "fullTime": 9, "partTime": 18 } },
    "sales": {
      "salesByCategory": [
        { "categoryName": "Stockings", "totalSales": 25731 }
      ],
      "revenue": 25731
    },
    "promotionEvents": [
      {
        "eventName": "Mega Savings Extravaganza",
        "promotionalDates": {
          "startDate": { "Year": 2023, "Month": 6, "Day": 29 },
          "endDate": { "Year": 2023, "Month": 7, "Day": 7 }
        },
        "discounts": [
          { "categoryName": "Stockings", "discountPercentage": 16 },
          { "categoryName": "Tree Ornaments", "discountPercentage": 8 }
        ]
      }
    ],
    "company": "Lakeshore Retail",
    "city": "Marvinfort",
    "storeOpeningDate": "2024-10-01T18:24:02.586Z",
    "lastUpdated": "2024-10-02T18:24:02.000Z"
  },
  {
    "_id": "923d2228-6a28-4856-ac9d-77c39eaf1800",
    "name": "Lakeshore Retail | Home Decor Hub - Franciscoton",
    "location": { "lat": 61.3945, "lon": -3.6196 },
    "staff": { "employeeCount": { "fullTime": 7, "partTime": 6 } },
    "sales": {
      "salesByCategory": [
        { "categoryName": "Lamps", "totalSales": 19880 },
        { "categoryName": "Rugs", "totalSales": 20055 }
      ],
      "revenue": 39935
    },
    "promotionEvents": [
      {
        "eventName": "Unbeatable Markdown Mania",
        "promotionalDates": {
          "startDate": { "Year": 2024, "Month": 3, "Day": 25 },
          "endDate": { "Year": 2024, "Month": 4, "Day": 1 }
        },
        "discounts": [
          { "categoryName": "Vases", "discountPercentage": 8 },
          { "categoryName": "Lamps", "discountPercentage": 5 }
        ]
      }
    ],
    "company": "Lakeshore Retail",
    "city": "Franciscoton",
    "lastUpdated": "2024-12-02T12:01:46.000Z",
    "storeOpeningDate": "2024-09-03T07:21:46.045Z"
  }

Example 2: Check for nested field existence

This example finds stores that have full-time employee count information.

db.stores.find(
 { "staff.employeeCount.fullTime": { $exists: true }},
 { "_id": 1, "staff.employeeCount": 1 }).limit(2)

The query returns stores where the nested field staff.employeeCount.fullTime exists.

  {
    "_id": "a715ab0f-4c6e-4e9d-a812-f2fab11ce0b6",
    "staff": {
      "employeeCount": {
        "fullTime": 9,
        "partTime": 18
      }
    }
  },
  {
    "_id": "923d2228-6a28-4856-ac9d-77c39eaf1800",
    "staff": {
      "employeeCount": {
        "fullTime": 7,
        "partTime": 6
      }
    }
  }

Related content