Articles → MONGODB → $First And $Last Aggregation Operators In Mongodb

$First And $Last Aggregation Operators In Mongodb

In this article, we will discuss the $first and the $last aggregation operators in MongoDB.

Purpose

The $first aggregation operator is used to get the first element in the groups of elements.

The $last aggregation operator is used to get the last element in the groups of elements.

Example

Consider the following collection: -

Picture showing the sample documents in mongodb

For the above collection, we will group the documents based on the customerId field. Once we group the collection, there will be 2 groups one for A123 and the other for B456.

To get the first element from the group, we will use the following query: -

db.orders.aggregate([   
    {
        $group: {
            _id: "$customerId",
            firstOrderId: { $first: "$_id" }
        }
    }
])

Picture showing the output of $first aggregation operator in mongodb

And to get the last element in the group, we will use the following query: -

db.orders.aggregate([   
    {
        $group: {
            _id: "$customerId",
            firstOrderId: { $last: "$_id" }
        }
    }
])

Picture showing the output of $last aggregation operator in mongodb

Posted By -	Karan Gupta

Posted On -	Friday, June 7, 2024

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