$all operator for matching all elements in MongoDB - Mini Project: Build & Apply

$all Operator for Matching All Elements in MongoDB

📖 Scenario: You are managing a small online bookstore database. Each book document contains a list of genres it belongs to. You want to find books that belong to all the genres a customer is interested in.

🎯 Goal: Build a MongoDB query using the $all operator to find books that match all specified genres.

📋 What You'll Learn

Create a collection called books with documents containing title and genres fields.

Define a variable desiredGenres that lists the genres to match.

Write a query using the $all operator to find books that have all genres in desiredGenres.

Complete the query so it can be run to retrieve matching books.

💡 Why This Matters

🌍 Real World

Online stores, libraries, or content platforms often need to find items that match all user-selected categories or tags.

💼 Career

Understanding $all queries is essential for database developers and analysts working with MongoDB or similar NoSQL databases to filter data precisely.

1

DATA SETUP: Create the books collection with sample documents

Create a variable called books that is an array of three documents. Each document should have a title string and a genres array of strings. Use these exact entries: { title: "The Adventure", genres: ["Adventure", "Fantasy"] }, { title: "Mystery Manor", genres: ["Mystery", "Thriller"] }, and { title: "Fantasy World", genres: ["Fantasy", "Adventure", "Magic"] }.

MongoDB

// Create the books array with the specified documents
// Your code here

Need a hint?

Use an array of objects with title and genres keys exactly as shown.

2

CONFIGURATION: Define the desiredGenres array to match

Create a variable called desiredGenres and set it to an array containing the strings "Adventure" and "Fantasy".

MongoDB

const books = [
  { title: "The Adventure", genres: ["Adventure", "Fantasy"] },
  { title: "Mystery Manor", genres: ["Mystery", "Thriller"] },
  { title: "Fantasy World", genres: ["Fantasy", "Adventure", "Magic"] }
];

// Define desiredGenres array with "Adventure" and "Fantasy"
// Your code here

Need a hint?

Use an array with the exact two strings inside.

3

CORE LOGIC: Write the MongoDB query using $all to find matching books

Create a variable called query and set it to an object that uses the $all operator on the genres field with the value of desiredGenres.

MongoDB

const books = [
  { title: "The Adventure", genres: ["Adventure", "Fantasy"] },
  { title: "Mystery Manor", genres: ["Mystery", "Thriller"] },
  { title: "Fantasy World", genres: ["Fantasy", "Adventure", "Magic"] }
];

const desiredGenres = ["Adventure", "Fantasy"];

// Create the query object using $all on genres with desiredGenres
// Your code here

Need a hint?

Use { genres: { $all: desiredGenres } } exactly.

4

COMPLETION: Add the final code to find matching books using the query

Create a variable called matchingBooks and set it to the result of filtering books where each book's genres array includes all elements in desiredGenres. Use Array.prototype.filter and every methods.

MongoDB

const books = [
  { title: "The Adventure", genres: ["Adventure", "Fantasy"] },
  { title: "Mystery Manor", genres: ["Mystery", "Thriller"] },
  { title: "Fantasy World", genres: ["Fantasy", "Adventure", "Magic"] }
];

const desiredGenres = ["Adventure", "Fantasy"];

const query = { genres: { $all: desiredGenres } };

// Filter books to find those matching all genres in desiredGenres
// Your code here

Need a hint?

Use books.filter with desiredGenres.every inside the callback.