mongodb group values by multiple fields

MongoDB Group Values by Multiple Fields: A Complete Guide

Are you struggling to group values by multiple fields in MongoDB? 🤷‍♀️ Don't worry, we've got you covered! In this blog post, we will address the common issues you may encounter and provide easy solutions to help you achieve your desired results. Let's dive in! 💪

The Problem: Grouping Values by Multiple Fields

Let's say you have a collection of documents similar to the ones provided in the context. You want to make a request that will describe the top N addresses and the top M books per address. The example of the expected result clearly shows that you want to group the values by both "addr" and "book" fields.

The Solution: Aggregation Framework to the Rescue! 🚀

MongoDB's Aggregation Framework comes to the rescue when it comes to complex operations like grouping values by multiple fields. Here's how you can achieve the desired result:

db.collection.aggregate([
  {
    $group: {
      _id: {
        addr: "$addr",
        book: "$book"
      },
      count: { $sum: 1 }
    }
  },
  {
    $group: {
      _id: "$_id.addr",
      books: {
        $push: {
          book: "$_id.book",
          count: "$count"
        }
      },
      total: { $sum: "$count" }
    }
  },
  {
    $sort: {
      total: -1
    }
  },
  {
    $limit: N
  }
])

Let's break down the solution step-by-step:

1. The first $group stage groups the documents based on the "addr" and "book" fields, and calculates the count of each combination using $sum.

2. The second $group stage groups the previous result by the "addr" field, and creates an array of books using $push. Each book object in the array includes the "book" field and its count.

3. The third $group stage calculates the total count of books per address using $sum.

4. The $sort stage sorts the result by the total count in descending order.

5. Finally, the $limit stage allows you to limit the result to the top N addresses.

The Result: Easily Understandable and Share-Worthy! 💡

With the above solution, you can easily group values by multiple fields and obtain the desired result. The example of the expected result demonstrates how the addresses and their respective books are displayed in a clear and organized manner.

Conclusion: Embrace the Power of Aggregation! 💥

Next time you find yourself in a situation where you need to group values by multiple fields in MongoDB, don't panic! Remember to leverage the Aggregation Framework and follow the step-by-step solution provided in this blog post. 🙌

Now it's your turn! Have you encountered any challenges while grouping values by multiple fields in MongoDB? Share your thoughts and experiences in the comments below. Let's build a knowledge-sharing community together! 💬😊