How MongoDB scans documents - Try It Yourself

How MongoDB scans documents

📖 Scenario: You are working with a MongoDB collection that stores information about books in a library. You want to understand how MongoDB scans documents when you query the collection.

🎯 Goal: Build a simple MongoDB collection with book documents, add a filter condition, and perform a query to see how MongoDB scans documents.

📋 What You'll Learn

Create a MongoDB collection named library with three book documents

Add a filter variable called filter to select books published after 2010

Write a query using find() with the filter to scan documents

Add a projection to return only the title and author fields

💡 Why This Matters

🌍 Real World

MongoDB is widely used to store and query document data in web applications, content management, and analytics.

💼 Career

Understanding how MongoDB scans documents helps optimize queries and improve application performance in real-world projects.

1

Create the library collection with book documents

Create a MongoDB collection called library and insert these three documents exactly: { title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', year: 1925 }, { title: 'The Road', author: 'Cormac McCarthy', year: 2006 }, { title: 'The Martian', author: 'Andy Weir', year: 2014 }

MongoDB

// Insert the three book documents into the library collection
// Your code here

Need a hint?

Use db.library.insertMany() with an array of three book objects.

2

Add a filter to select books published after 2010

Create a variable called filter that selects documents where the year field is greater than 2010

MongoDB

db.library.insertMany([
  { title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', year: 1925 },
  { title: 'The Road', author: 'Cormac McCarthy', year: 2006 },
  { title: 'The Martian', author: 'Andy Weir', year: 2014 }
])

// Create a filter to find books with year > 2010
// Your code here

Need a hint?

Use { year: { $gt: 2010 } } as the filter object.

3

Query the library collection using the filter

Write a query using db.library.find(filter) to scan documents matching the filter

MongoDB

db.library.insertMany([
  { title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', year: 1925 },
  { title: 'The Road', author: 'Cormac McCarthy', year: 2006 },
  { title: 'The Martian', author: 'Andy Weir', year: 2014 }
])

const filter = { year: { $gt: 2010 } }

// Query the library collection with the filter
// Your code here

Need a hint?

Use db.library.find(filter) to get documents matching the filter.

4

Add a projection to return only title and author

Modify the query to include a projection that returns only the title and author fields by using db.library.find(filter, { title: 1, author: 1, _id: 0 })

MongoDB

db.library.insertMany([
  { title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', year: 1925 },
  { title: 'The Road', author: 'Cormac McCarthy', year: 2006 },
  { title: 'The Martian', author: 'Andy Weir', year: 2014 }
])

const filter = { year: { $gt: 2010 } }

// Modify the query to return only title and author fields
// Your code here

Need a hint?

Use the second argument in find() to specify the projection fields.