MongoDB Operators API Reference

`Operators`

5 methods

Common query and pipeline operators.

{ $match: <query> }

Aggregation stage that filters documents, behaving like a collection find query.

Name	Type	Description
query	object	Selector document.

Stage

mongodb

{ $match: { status: 'active', age: { $gte: 18 } } }

{ $group: { _id: <expr>, <field>: { <accumulator>: <expr> } } }

Aggregation stage that groups documents by _id expression and applies accumulators per field.

Name	Type	Description
_id	expression	Group key expression; null groups all documents.
accumulator	string	$sum, $avg, $max, $min, $push, $addToSet, etc.

Stage

mongodb

{ $group: { _id: '$dept', avgSalary: { $avg: '$salary' } } }

{ $project: <specification> }

Aggregation stage that passes only specified fields (with optional computed values) downstream.

Name	Type	Description
specification	object	Field inclusion (1), exclusion (0) or expression.

Stage

mongodb

{ $project: { name: 1, age: 1, _id: 0 } }

{ $lookup: { from, localField, foreignField, as } }

Performs a left outer join to another collection in the same database.

Name	Type	Description
from	string	Foreign collection name.
localField	string	Field from the input documents.
foreignField	string	Field from the foreign collection documents.
as	string	Output array field name.

Stage

mongodb

{ $lookup: { from: 'orders', localField: '_id', foreignField: 'userId', as: 'orders' } }

{ $sort: { <field>: 1 | -1 } }

Aggregation stage that sorts documents by the given fields; 1 ascending, -1 descending.

Name	Type	Description
field	string	Field path to sort by.

Stage

mongodb

{ $sort: { createdAt: -1 } }