MongoDB Aggregation Pipelines

MongoDB Tutorial

About Lesson

Introduction

Learn how to perform complex data aggregation operations in MongoDB using the aggregation pipeline framework.

Connecting to MongoDB

Before starting aggregation operations, ensure you are connected to your MongoDB server:

Example: Connecting to MongoDB

mongosh

This command starts the mongosh shell and connects to the default MongoDB server running locally.

Switching to a Database

Switch to the database where your collection resides using the use command:

Example: Switching to a Database

use mydatabase

This command switches to the “mydatabase” database. Replace mydatabase with your database name.

Aggregation Pipeline Stages

Construct aggregation pipelines using various stages:

$match: Filters documents based on specified criteria.
$group: Groups documents by a specified identifier.
$project: Reshapes documents by including, excluding, or adding fields.
$sort: Sorts documents based on specified fields.
$limit: Limits the number of documents passed to the next stage.
$skip: Skips a specified number of documents before passing to the next stage.
$unwind: Deconstructs an array field from documents and outputs one document for each element.

Examples

Here are some examples of MongoDB aggregation pipelines:

Example: Aggregating Data

db.mycollection.aggregate([
    { $match: { status: "active" } },
    { $group: { _id: "$category", total: { $sum: "$quantity" } } }
])

This pipeline filters documents where status is “active”, groups them by category, and calculates the total quantity for each category.

Example: Sorting Results

db.mycollection.aggregate([
    { $sort: { age: 1 } }
])

This pipeline sorts documents in ascending order based on the age field.

Executing Aggregation

Execute aggregation pipelines using the aggregate method:

Example: Executing Aggregation

db.mycollection.aggregate(pipeline)

Replace pipeline with your aggregation pipeline array defined earlier.

Conclusion

The MongoDB aggregation framework provides powerful tools for data aggregation, allowing you to perform complex operations directly within the database. Experiment with different stages and operators to achieve the desired data transformations and analysis.

Join the conversation