MongoDB — Aggregation Pipeline

Pipeline Concept

Documents pass through stages sequentially.

Common Stages

$match

{ $match: { status: "active" } }

$group

{ $group: { _id: "$category", total: { $sum: "$amount" } } }

$sort

{ $sort: { total: -1 } }

$project

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

$limit and $skip

{ $skip: 10 }
{ $limit: 5 }

$unwind

{ $unwind: "$hobbies" }

Accumulators

Accumulator	Description
$sum	Sum values
$avg	Average
$min	Minimum
$max	Maximum
$first	First element
$last	Last element

Example Pipeline

db.orders.aggregate([
  { $match: { status: "completed" } },
  { $unwind: "$items" },
  { $group: { 
    _id: "$userId", 
    totalSpent: { $sum: "$items.price" } 
  }},
  { $sort: { totalSpent: -1 } },
  { $limit: 10 }
]);

Mini Practice

1. Build a pipeline
2. Use multiple stages
3. Calculate aggregates
4. Unwind arrays

Up Next

Continue with Group — grouping documents.