For an individual document, $first returns the first element of the array. This is the case with stages like $addFields .

For an individual document, $first returns the first element of the array. This is the case with stages like $addFields .

8 июл. 2024 г. · The $first operator is particularly useful when you need to retrieve the first document from each group in an aggregation pipeline based on a ...

Definition. $first. Returns the value that results from applying an expression to the first document in a group of documents that share the same group by key.

Returns the value that results from applying an expression to the first document in a group of documents. Only meaningful when documents are in a defined ...

19 дек. 2015 г. · In my MongoDB people collection I need to filter people with the same 'alias' property value, keeping the first one of them, and also keeping all people with a ... Can I get first document (not field) in MongoDB aggregate query? MongoDB get first and last document in aggregate query Другие результаты с сайта stackoverflow.com

When using $first in a $group stage, the $group stage should follow a $sort stage to have the input documents in a defined order.

$first has the following syntax: { $first: <expression> } The <expression> can be any valid expression as long as it resolves to an array, null or missing.

$first selects the first document from each output group: The _id: null group is included. When the accumulator field, $quantity in this example, is missing ...

The following page describes the array element operator $first . For the accumulator $first , available only with the $group stage, see $first (accumulator) ...