Aggregate

Learn the Mongoose aggregate pipeline.

What is Aggregate?

Aggregate is MongoDB's pipeline-based data processing tool. It passes documents through stages to group, filter, sort, and compute. This enables complex analytics that simple queries cannot do.

The pipeline is an array of stages. Each stage takes documents, processes them, and passes them to the next. For example [{ $match: { age: { $gt: 18 } } }, { $group: { _id: "$city", count: { $sum: 1 } } }] first filters adults, then groups by city. You run it with Model.aggregate(pipeline).

Aggregate stages

Each pipeline stage starts with an operator. $match filters documents (like find). $group groups documents by a key and computes ($sum, $avg). $sort sorts. $count gives the document count.

Stages run in array order; the order matters. Filtering with $match first reduces the document count, so later stages run faster. This is critical for performance on large datasets.

Exercise Log the type of aggregate

Import mongoose. Create a model with mongoose.model("User", { name: String }). Log typeof User.aggregate.

Show example solution

const mongoose = require("mongoose");
const User = mongoose.model("User", { name: String });
console.log(typeof User.aggregate);

Test yourself

Complete the method name

const results = await User.____([{ $match: {} }])

Show answer

const results = await User.aggregate([{ $match: {} }])

Match each piece to its role

$match

Filters
$group

Groups
$sort

Sorts
$count

Counts
What parameter does aggregate take?
- An array of stages
- Bir dize
- A number
- Bir fonksiyon
Show answer

An array of stages — aggregate takes an array of stages.

Next lesson: Summary - MongoDB

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