$in

The $in operator matches values of a field against an array of possible values. The $in operator filters documents where the value of a field equals any of the specified values.

Syntax

{
    field: {
        $in: [ listOfValues ]
    }
}

Parameters

Parameter Description
field The field to match
[listOfValues] An array of values to match against the specified field

Examples

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

{
  "_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"
  ],
  "company": "Lakeshore Retail",
  "city": "Port Cecile",
  "lastUpdated": {
    "$date": "2024-12-11T10:21:58.274Z"
  }
}

Example 1 - Use $in operator as comparison-query to find a store with specific categories of promotions

The query finds stores that offer discounts in either "Smoked Salmon" or "Anklets" categories via promotion events.

db.stores.find(
  {
    "promotionEvents.discounts.categoryName": {
      "$in": ["Smoked Salmon", "Anklets"]
    }
  },
  {
    "name": 1,
    "promotionEvents.discounts.categoryName": 1
  }
).limit(1)

This returns the following result:

{
  "_id": "48fcdab8-b961-480e-87a9-19ad880e9a0a",
  "name": "Lakeshore Retail | Jewelry Collection - South Nicholas",
  "promotionEvents": [
    {
      "discounts": [
        {"categoryName": "Anklets"},
        {"categoryName": "Cufflinks"}
      ]
    },
    {
      "discounts": [
        {"categoryName": "Anklets"},
        {"categoryName": "Brooches"}
      ]
    },
    {
      "discounts": [
        {"categoryName": "Rings"},
        {"categoryName": "Bracelets"}
      ]
    },
    {
      "discounts": [
        {"categoryName": "Charms"},
        {"categoryName": "Bracelets"}
      ]
    },
    {
      "discounts": [
        {"categoryName": "Watches"},
        {"categoryName": "Pendants"}
      ]
    }
  ]
}

Example 2 - Use $in operator as array-expression in an array for a specified value or set of values

The query searches for the specified store and filters documents where at least one discountPercentage within any promotionEvents.discounts is either 15 or 20. It uses a dot notation path and the $in operator to match nested discount values across the array hierarchy.

db.stores.find(
  {
    "_id": "48fcdab8-b961-480e-87a9-19ad880e9a0a",
    "promotionEvents.discounts.discountPercentage": { $in: [15, 20] }
  },
  {
    "_id": 1,
    "name": 1,
    "promotionEvents.discounts": 1
  }
)

The query returns document where the discounts array contains any element with a discountPercentage of either 15 or 20, and only shows the complete discounts array for those documents.

{
  "_id": "48fcdab8-b961-480e-87a9-19ad880e9a0a",
  "name": "Lakeshore Retail | Jewelry Collection - South Nicholas",
  "promotionEvents": [
    {
      "discounts": [
        { "categoryName": "Anklets", "discountPercentage": 12 },
        { "categoryName": "Cufflinks", "discountPercentage": 9 }
      ]
    },
    {
      "discounts": [
        { "categoryName": "Anklets", "discountPercentage": 23 },
        { "categoryName": "Brooches", "discountPercentage": 12 }
      ]
    },
    {
      "discounts": [
        { "categoryName": "Rings", "discountPercentage": 10 },
        { "categoryName": "Bracelets", "discountPercentage": 21 }
      ]
    },
    {
      "discounts": [
        { "categoryName": "Charms", "discountPercentage": 9 },
        { "categoryName": "Bracelets", "discountPercentage": 13 }
      ]
    },
    {
      "discounts": [
        { "categoryName": "Watches", "discountPercentage": 20 },
        { "categoryName": "Pendants", "discountPercentage": 7 }
      ]
    }
  ]
}

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