MongoDB Aggregation Framework: Real Examples Tutorial

Understanding the Aggregation Pipeline

An aggregation pipeline is a sequence of stages that process documents in a collection.

Each stage transforms the documents and passes the results to the next stage.

Common stages include $match for filtering, $group for aggregation, and $project for reshaping data.

• Stages execute in order, forming a pipeline.
• Each stage accepts input documents and outputs transformed documents.
• Pipelines can include multiple stages to perform complex operations.

Real Example 1: Filtering and Grouping Sales Data

Suppose you have a sales collection and want to find total sales per product category for orders in 2023.

You can use $match to filter by date and $group to sum sales amounts by category.

Real Example 2: Projecting Specific Fields and Calculated Values

You may want to reshape documents to include only certain fields and add computed fields.

The $project stage lets you specify which fields to include or exclude and create new fields.

Real Example 3: Combining Multiple Stages

Complex queries often combine multiple stages like $match, $group, $sort, and $limit.

This example finds the top 5 customers by total purchase amount.