Array update with $[] all positional in MongoDB - Mini Project: Build & Apply

Update All Elements in a MongoDB Array Using $[] Positional Operator

📖 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 rating and a comment. You want to update all reviews to increase their rating by 1 point.

🎯 Goal: Build a MongoDB update query that uses the $[] all positional operator to increment the rating field of every review in the reviews array for a specific book.

📋 What You'll Learn

Create a collection named books with one document containing a title and a reviews array with exactly two review objects.

Define a filter variable filter to select the book with the exact title 'Learn MongoDB'.

Write an update query using $inc and the $[] all positional operator to increment the rating of all reviews by 1.

Complete the update command by combining the filter and update variables in a db.books.updateOne() call.

💡 Why This Matters

🌍 Real World

Updating all elements in an array field is common when you want to apply the same change to every item, such as increasing ratings, marking all tasks as done, or resetting flags.

💼 Career

Knowing how to use the $[] positional operator is important for database developers and administrators working with MongoDB to efficiently update array data without multiple queries.

1

Create the books collection with one book document

Create a variable called books and assign it an array with one object. The object must have a title field set to 'Learn MongoDB' and a reviews array containing exactly two objects: the first with rating 3 and comment 'Good intro', the second with rating 4 and comment 'Very helpful'.

MongoDB

# Your code here

Need a hint?

Remember to create a list with one dictionary. The dictionary should have the exact keys and values as specified.

2

Define the filter to select the book by title

Create a variable called filter and assign it a dictionary that matches documents where the title is exactly 'Learn MongoDB'.

MongoDB

books = [{
    'title': 'Learn MongoDB',
    'reviews': [
        {'rating': 3, 'comment': 'Good intro'},
        {'rating': 4, 'comment': 'Very helpful'}
    ]
}]

# Your code here

Need a hint?

Use a dictionary with the key title and the exact string value.

3

Write the update query using $[] to increment all ratings

Create a variable called update and assign it a dictionary that uses $inc with the key 'reviews.$[].rating' set to 1 to increment all rating fields inside the reviews array.

MongoDB

books = [{
    'title': 'Learn MongoDB',
    'reviews': [
        {'rating': 3, 'comment': 'Good intro'},
        {'rating': 4, 'comment': 'Very helpful'}
    ]
}]

filter = {'title': 'Learn MongoDB'}

# Your code here

Need a hint?

Use the $inc operator with the key reviews.$[].rating to update all array elements.

4

Complete the update command with db.books.updateOne()

Write a line that calls db.books.updateOne() with the filter and update variables as arguments to update the document.

MongoDB

books = [{
    'title': 'Learn MongoDB',
    'reviews': [
        {'rating': 3, 'comment': 'Good intro'},
        {'rating': 4, 'comment': 'Very helpful'}
    ]
}]

filter = {'title': 'Learn MongoDB'}

update = {'$inc': {'reviews.$[].rating': 1}}

# Your code here

Need a hint?

Use db.books.updateOne(filter, update) to apply the update.