$first/$last
Reference group: Accumulators and ranking
What it does
Returns first/last encountered value; sort first when order matters.
Syntax
{$first: expression} / {$last: expression}
Use case
Select earliest/latest record.
$first/$last: practical example
{ $sort: { createdAt: 1 } }, { $group: { _id: "$customerId", firstOrder: { $first: "$$ROOT" } } }💡 Explanation
Returns first/last encountered value; sort first when order matters.
When to use it
Select earliest/latest record.
Key Takeaways
- Returns first/last encountered value; sort first when order matters.
- Typical use: Select earliest/latest record.