$in (array expression)

APPLIES TO: MongoDB vCore

The $in operator filters documents where a field's value matches any value in a specified array, making it ideal for matching multiple criteria. It's especially useful for querying nested arrays and handling complex data structures efficiently.

{
  field: { $in: [<value1>, <value2>, ...] }
}

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

{
  "_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5",
  "name": "Lakeshore Retail",
  "location": {
    "lat": -9.9399,
    "lon": -0.334
  },
  "staff": {
    "totalStaff": {
      "fullTime": 18,
      "partTime": 7
    }
  },
  "sales": {
    "totalSales": 35911,
    "salesByCategory": [
      {
        "categoryName": "DJ Headphones",
        "totalSales": 35911
      }
    ]
  },
  "promotionEvents": [
    {
      "discounts": [
        {
          "categoryName": "DJ Turntables",
          "discountPercentage": 18
        },
        {
          "categoryName": "DJ Mixers",
          "discountPercentage": 15
        }
      ]
    },
    {
      "discounts": [
        {
          "categoryName": "DJ Accessories",
          "discountPercentage": 18
        },
        {
          "categoryName": "DJ Mixers",
          "discountPercentage": 10
        }
      ]
    }
  ]
}

The example queries for document with specified _id that have DJ Mixers with a discount percentage of either 15 or 20 within the promotionEvents.discounts array.

db.stores.find({ "_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5"
                ,"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": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5",
  "name": "Lakeshore Retail",
  "promotionEvents": [
    {
      "discounts": [
        {
          "categoryName": "DJ Turntables",
          "discountPercentage": 18
        },
        {
          "categoryName": "DJ Mixers",
          "discountPercentage": 15
        }
      ]
    }
  ]
}

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