MongoDB 4.2 - Returns the first n elements from an array

Question

In MongoDB 5.2, there is a function called $firstN. Is there any alternate function or any other way to find the first n elements from a given array in MongoDB 4.2?

Sample document:

{
    "id": 1234,
    "products": [
      {
        "productId": 111,
        "path": "H"
      },
      {
        "productId": 112,
        "path": "H"
      },
      {
        "productId": 113,
        "path": "P"
      }
    ]
}

I want to return the first n product objects from the product array.

With MongoDB 5.2, I can solve this Mongo playground.

Answer 1

Use $slice operator with a similar functionality to take the nth element.

db.collection.aggregate([
  {
    "$project": {
      "firstFiveProducts": {
        "$slice": [
          "$products",
          5
        ]
      }
    }
  }
])

Demo @ MongoPlayground