Array update with $[identifier] filtered in MongoDB - Mini Project: Build & Apply

Update Specific Items in a MongoDB Array Using $[identifier]

📖 Scenario: You manage a MongoDB collection that stores information about books in a library. Each book document contains an array of reviews, where each review has a reviewer name and a rating score.Sometimes, you need to update the rating given by a specific reviewer without changing other reviews.

🎯 Goal: Learn how to update only the reviews in the reviews array where the reviewer matches a specific name, using the $[identifier] filtered positional operator in MongoDB.

📋 What You'll Learn

Create a MongoDB document with a reviews array containing multiple review objects.

Define an array filter to target reviews by a specific reviewer name.

Use the $[identifier] filtered positional operator to update only the matching review's rating.

Complete the update operation with the correct filter and update syntax.

💡 Why This Matters

🌍 Real World

Updating specific items in arrays is common in applications like product reviews, user comments, or order items where only certain entries need changes without affecting others.

💼 Career

Knowing how to use array filters and the $[identifier] operator is essential for backend developers and database administrators working with MongoDB to write efficient and precise update queries.

1

Create a book document with a reviews array

Create a MongoDB document called book with the following fields: title set to "Learn MongoDB", and reviews as an array containing these objects exactly: { reviewer: "Alice", rating: 4 }, { reviewer: "Bob", rating: 5 }, and { reviewer: "Charlie", rating: 3 }.

MongoDB

// Create the book document with title and reviews array
// Your code here

Need a hint?

Define a constant book with the exact structure and values for title and reviews.

2

Define an array filter to target Bob's review

Create a variable called arrayFilters that is an array containing one filter object. This filter object should use the identifier elem and match reviews where elem.reviewer equals "Bob".

MongoDB

const book = {
  title: "Learn MongoDB",
  reviews: [
    { reviewer: "Alice", rating: 4 },
    { reviewer: "Bob", rating: 5 },
    { reviewer: "Charlie", rating: 3 }
  ]
};

// Define arrayFilters to target reviews by Bob
// Your code here

Need a hint?

Use const arrayFilters = [{ "elem.reviewer": "Bob" }]; to define the filter.

3

Write the update command using $[elem] to change Bob's rating

Write a MongoDB update command called updateCommand that uses $set to change reviews.$[elem].rating to 10. Use the arrayFilters variable you defined earlier in the update options.

MongoDB

const book = {
  title: "Learn MongoDB",
  reviews: [
    { reviewer: "Alice", rating: 4 },
    { reviewer: "Bob", rating: 5 },
    { reviewer: "Charlie", rating: 3 }
  ]
};

const arrayFilters = [{ "elem.reviewer": "Bob" }];

// Create updateCommand to set Bob's rating to 10 using $[elem]
// Your code here

Need a hint?

Use $set with the path reviews.$[elem].rating to update the rating.

4

Combine filter, update, and arrayFilters in the final update operation

Write a variable called finalUpdate that is an object containing these keys: filter to find the book by title "Learn MongoDB", update set to updateCommand, and options set to an object with arrayFilters equal to the arrayFilters variable.

MongoDB

const book = {
  title: "Learn MongoDB",
  reviews: [
    { reviewer: "Alice", rating: 4 },
    { reviewer: "Bob", rating: 5 },
    { reviewer: "Charlie", rating: 3 }
  ]
};

const arrayFilters = [{ "elem.reviewer": "Bob" }];

const updateCommand = {
  $set: { "reviews.$[elem].rating": 10 }
};

// Create finalUpdate object with filter, update, and options
// Your code here

Need a hint?

Combine the filter, update, and options with arrayFilters into one object called finalUpdate.