Faceted Aggregation in MongoDB

1. Introduction

Faceted aggregation is a powerful feature in MongoDB that allows you to perform multiple aggregations on a dataset and return results in a structured format. This technique is commonly used in e-commerce applications for product filtering and categorization.

2. Key Concepts

2.1 Aggregation Pipeline

The aggregation pipeline is a framework that allows you to process data records and return computed results. It consists of stages that transform the data as it passes through the pipeline.

2.2 Facets

In the context of faceted aggregation, a facet represents a unique way of grouping and summarizing the data, often used for filtering or categorizing results.

3. Step-by-Step Process

Note: Ensure you have MongoDB installed and running to execute the examples below.

3.1 Sample Data

Consider a collection named products:

{
        "_id": 1,
        "name": "Laptop",
        "category": "Electronics",
        "price": 1200,
        "brand": "BrandA"
    }

3.2 Using the Aggregation Framework

To perform faceted aggregation:

db.products.aggregate([
        {
            $facet: {
                "categoryCounts": [
                    { $group: { _id: "$category", count: { $sum: 1 } } }
                ],
                "brandCounts": [
                    { $group: { _id: "$brand", count: { $sum: 1 } } }
                ]
            }
        }
    ])

3.3 Explanation of the Code

The above code performs the following:

Uses the $facet stage to create multiple pipelines.
Groups the products by category and counts them.
Groups the products by brand and counts them.

4. Best Practices

Keep your facets simple to enhance performance.
Limit the number of documents processed in each facet using $match before aggregation.
Benchmark your queries to identify performance bottlenecks.

5. FAQ

What is the maximum number of facets I can use?

MongoDB does not impose a strict limit on the number of facets, but performance may degrade with excessive facets.

Can I apply sorting within facets?

Yes, you can apply sorting using the $sort stage in each facet pipeline.