MongoDB Aggregation Pipeline Guide

The MongoDB aggregation pipeline is a powerful framework for data processing and analysis. In this guide, we'll cover the most useful stages and how to combine them effectively.

Core Stages

$match

Filters documents, similar to find(), but should be used early in the pipeline to reduce the number of documents being processed.

$group

Groups documents by a specified expression and applies accumulator functions like $sum, $avg, and $push.

$lookup

Performs a left outer join with another collection, enabling you to combine data from multiple collections.

$project

Reshapes documents by including, excluding, or adding new fields.

Best Practices

• Place $match and $limit stages early in the pipeline
• Use indexes on fields used in $match and $sort stages
• Avoid using $unwind on large arrays when possible
• Use $lookup sparingly as it can be expensive

Conclusion

The aggregation pipeline is one of MongoDB's most powerful features. Mastering it will enable you to perform complex data analysis directly in your database.