Question 360047 in Mongodb Question posted in
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How can I get the first and the last element from MongoDB collection?

I have a mongodb collection called "Users" and I want to create a query to get the first and the last document from this collection based in a datetime field called InsertedAt.
I know how to get the first and the last element using sort, but I want to return both records in one query, like this:

[
    {
        _id: ObjectId("65c656fd8651a89640db013a"),
        insertedAt: ISODate("2023-02-01T16:46:33.166Z"), // First record of collection
        name: "Bob Jhonson"
    },
    {
        _id: ObjectId("65c4d88a2a06618ad4e972f4"),
        insertedAt: ISODate("2023-03-11T12:16:33.166Z"), // Last record of collection
        name: "Bob Jhonson"
    }
]

How can I do this?

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2

Answers


  1. 0

    Just chain up your 2 queries with $unionWith

    db.collection.aggregate([
  {
    "$sort": {
      "insertedAt": 1
    }
  },
  {
    $limit: 1
  },
  {
    "$unionWith": {
      "coll": "collection",
      "pipeline": [
        {
          "$sort": {
            "insertedAt": -1
          }
        },
        {
          $limit: 1
        }
      ]
    }
  }
])

    Mongo Playground

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  2. 0

    the response is not exactly as the format as you want but you can do it with only one sort and a group stage

    test it here

    db.collection.aggregate([
  {
    "$sort": {
      "InsertedAt": 1
    }
  },
  {
    "$group": {
      "_id": null,
      "first": {
        "$first": "$$ROOT"
      },
      "last": {
        "$last": "$$ROOT"
      }
    }
  },
  {
    "$project": {
      _id: 0
    }
  }
])
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