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Fixed aggregation exercises
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‎docs/10-intro.mdx

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import Tabs from "@theme/Tabs";
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import TabItem from "@theme/TabItem";
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| Lab goals | Learn about aggregation pipelines writing aggregation pipelines |
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| Lab goals | Learn about MongoDB's Query API including Aggregation Framework |
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| ----------------- | ----------------------------------------------------------------------------------- |
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| What you'll learn | What are aggregation pipelines? |
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| | How are they different from simple MongoDB queries or SQL? |
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| What you'll learn | CRUD Operations in MongoDB vs SQL |
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| | Aggregation Framework in MongoDB |
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| | How to use simple pipelines to get data, filter it, show the fields needed |
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| | How to write more advanced pipelines, querying arrays, counting and sorting results |
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| | How to do JOINs using $lookup |
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| | How to group data |
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| | Exporting data |
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| | How to write aggregations using popular programming languages (TBD) |
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| Time to complete | 90 mins |
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In the navigation bar and on some pages, you will notice some icons. Here are their meanings:

‎docs/40-CRUD/2-SELECT.mdx

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---
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## **Exercises**
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👐 **Retrieve only the `title` field for all books.**
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👐 **Fetch only `title` and `totalInventory` for books with more than 500 pages.**
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👐 **Retrieve all fields except `_id` and `authors` for books in the "History" genre.**
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👐 **Find all books written by "Isaac Asimov" and return only `title` and `available` copies.**
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👐 **Exclude `reviews` and `attributes` from the query results.**
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---
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## **Challenge**
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### 👐 1. Retrieve only the `title` field for all books.
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<details>
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<summary>Answer</summary>
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<div>
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```js
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db.books.find({}, {title: 1, _id: 0});
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```
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</div>
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</details>
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### 👐 2. Retrieve all fields except `_id` and `authors` for books in the "History" genre.
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<details>
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<summary>Answer</summary>
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<div>
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```js
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db.books.find({genres: "History"}, {_id: 0, authors: 0});
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```
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</div>
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</details>

‎docs/40-CRUD/3-ORDER-BY-SORT.mdx renamed to ‎docs/40-CRUD/3-ORDER-LIMIT.mdx

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@@ -58,10 +58,15 @@ This returns the **top 10 available books** in the "Science Fiction" genre.
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---
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## **Exercises**
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👐 Retrieve the top 3 books with the most reviews.
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👐 Find the **first 10 books** alphabetically by `title`.
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👐 Get the **latest 5 books** added to the database (assume a `createdAt` field).
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👐 Find **the 2 oldest authors** (assume a `birthYear` field).
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👐 Retrieve **the top 7 books** with the highest `rating`.
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## Challenge
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### 👐 1. Find the first 10 books alphabetically by `title`.
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<details>
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<summary>Answer</summary>
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<div>
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```js
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db.books.find({}).sort({title: 1}).limit(10)
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```
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</div>
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</details>

‎docs/40-CRUD/4-INSERT-DELETE.mdx

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DELETE FROM reviews WHERE bookId = '0786222727';
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```
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## Exercises
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- 👐 Insert 4 more reviews for `bookId` "0786222727".
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- 👐 Delete all the reviews for `bookId` "0786222727" through a single command.
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## Challenge
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### 👐 1. Insert 4 more reviews for `bookId` "0786222727".
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<details>
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<summary>Answer</summary>
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<div>
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```js
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db.books.insertMany([
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{
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text: "Thrilling end.",
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rating: 4,
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name: "Mark",
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bookId: "0786222727",
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},
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{
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text: "Must read!",
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rating: 5,
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name: "Raj",
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bookId: "0786222727",
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},
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{
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text: "Very expensive",
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rating: 3,
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name: "Yun",
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bookId: "0786222727",
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},
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{
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text: "Extremely satisfied with the storyline!",
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rating: 5,
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name: "Lisa",
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bookId: "0786222727",
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}
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]);
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```
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</div>
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</details>
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### 👐 2. Delete all the reviews for `bookId` "0786222727" through a single command.
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<details>
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<summary>Answer</summary>
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<div>
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```js
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db.books.deleteMany({"bookId": "0786222727"})
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```
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</div>
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</details>

‎docs/40-CRUD/5-UPDATE.mdx

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---
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## Exercises
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- 👐 Update the pages of "NoSQL Guide" to 450.
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- 👐 Update all books published before 2000 to have isClassic: true.
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- 👐 What happens if no document matches the update query?
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## Challenge
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### 👐 1. Update the pages of the book "Treasure of the Sun" to 449.
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<details>
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<summary>Answer</summary>
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<div>
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```js
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db.books.updateOne(
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{"title": "Treasure of the Sun"},
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{$set: {pages: 449}}
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);
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```
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</div>
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</details>

‎docs/50-aggregation/2-match-project.mdx

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---
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### **Exercise 🚀**
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👐 Find books with more than 10 available copies.
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👐 Return only book titles and publication year.
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👐 Create a computed field `stockStatus`: "In Stock" if available > 0, otherwise "Out of Stock".
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---
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🔹 **Next Up: Understanding $group and $sort!**
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## Challenge 🚀
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### 👐 1. Find books with more than 2 available copies.
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<details>
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<summary>Answer</summary>
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<div>
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```js
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db.books.aggregate([
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{ $match: {available: {$gt: 2}}}
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]);
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```
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</div>
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</details>
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### 👐 2. Find books with more than 2 available copies, return only book titles and publication year.
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<details>
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<summary>Answer</summary>
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<div>
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```js
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db.books.aggregate([
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{ $match: {available: {$gt: 2}}},
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{ $project: {title: 1, year: 1, _id: 0}}
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]);
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```
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</div>
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</details>

‎docs/50-aggregation/3-sort-limit.mdx

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### 👐 Challenge: After the year 2010, which book has the most number of authors.
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### 👐 Challenge
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## 👐 1. After the year 2010, which book has the most number of authors.
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<details>
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<summary>Answer</summary>

‎docs/50-aggregation/4-GROUP-BY.mdx renamed to ‎docs/50-aggregation/4-group.mdx

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import Tabs from "@theme/Tabs";
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import TabItem from "@theme/TabItem";
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# 👐 $group
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In SQL, the GROUP BY statement groups rows that have the same values into summary rows, like "find the number of customers in each country".
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---
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## 👐 Exercise
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👐 Find the total number of reviews each book has received.
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👐 Get the highest rating given to each book.
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👐 Count the number of authors who have written at least one book.
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## 👐 Challenge
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### 👐 1. Find the total number of pages published every year.
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<details>
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<summary>Answer</summary>
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```js
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db.books.aggregate([
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{
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$group: {
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_id: "$year",
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totalPages: { $sum: "$pages" }
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}
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},
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]);
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```
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</details>
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### 👐 2. Find users with the most number of reviews. Hint: Use the `name` field in the reviews collection.
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<details>
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<summary>Answer</summary>
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There are 2 ways to solve this-
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- $group with $sort
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- $sortByCount
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<Tabs groupId="aggregations">
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<TabItem value="atlas" label="$group with $sum + $sort">
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```js
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db.reviews.aggregate([
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{
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$group: {
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_id: "$name",
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totalReviews: { $sum: 1 },
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},
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},
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{
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$sort: {
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totalReviews: -1,
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},
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},
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]);
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```
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</TabItem>
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<TabItem value="mongodb-shell" label="$sortByCount">
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```js
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db.reviews.aggregate([
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{
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$sortByCount: "$name",
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},
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]);
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```
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</TabItem>
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</Tabs>
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</details>

‎docs/50-aggregation/5-JOIN.mdx

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## 🔹 Joining 2 collections
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### 👐 Example 1: Joining Authors collection with Books\*\*
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### 👐 Example 1: Joining Authors collection with Books
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🔍 **Get book details along with their authors**
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🔍 Get book details along with their authors
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```js
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db.authors.aggregate([
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Since `$lookup` produces an **array**, we can flatten it using `$unwind`.
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### Example 2: Get Book Titles and Single Author Name
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### Example 2: Get Only Book Titles and Single Author Name
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```js
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db.authors.aggregate([
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```
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:::info
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The $lookup operation creates an array within each book document. Using $unwind then flattens this array, resulting in a separate document for every book and each author.
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The $lookup operation creates an array within each book document. Using $unwind then flattens this array, resulting in a separate document for every single book - author pair.
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:::
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---
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## **🚀 Exercise**
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👐 Fetch books with their associated reviews.
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👐 Get authors and the books they have written.
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👐 Use `$unwind` to show each book-author pair separately.
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## 👐 Challenge
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### 👐 1. Fetch books with their associated reviews
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<details>
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<summary>Answer</summary>
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```js
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db.books.aggregate([
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{
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$lookup:
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{
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from: "reviews",
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localField: "_id",
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foreignField: "bookId",
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as: "reviews"
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}
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}
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]);
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```
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</details>

‎docs/50-aggregation/7-CREATE-VIEW.mdx

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## **🔹 Exercise 🚀**
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## 👐 Challenge
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👐 Create a `top_rated_books` collection that stores books with an average rating above 4.5.
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👐 Maintain a `review_stats` collection that contains the total number of reviews per book.
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👐 Update the `borrowed_books_summary` collection by storing the total borrowed count for each book.
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---
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🚀 **Next Up: Optimizing Aggregation Pipelines!**
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<details>
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<summary>Answer</summary>
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```js
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db.books.aggregate([
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{
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$lookup:
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{
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from: "reviews",
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localField: "_id",
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foreignField: "bookId",
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as: "reviews"
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}
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}
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]);
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```
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</details>

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