$limit and $skip stages in MongoDB - Mini Project: Build & Apply

$limit and $skip stages in MongoDB aggregation

📖 Scenario: You are managing a small online bookstore database. You want to show customers a limited number of books per page and skip some books to create pages.

🎯 Goal: Build a MongoDB aggregation pipeline that uses $limit and $skip stages to paginate the list of books.

📋 What You'll Learn

Create a collection called books with 5 specific book documents.

Add a variable pageSize to control how many books show per page.

Add a variable pageNumber to control which page of books to show.

Write an aggregation pipeline using $skip and $limit to get the correct page of books.

💡 Why This Matters

🌍 Real World

Pagination is used in websites and apps to show data in small chunks, making it easier to browse large lists like books, products, or messages.

💼 Career

Knowing how to use <code>$limit</code> and <code>$skip</code> in MongoDB is essential for backend developers and database administrators to efficiently handle large datasets and improve user experience.

1

Create the books collection with 5 book documents

Create a MongoDB collection called books and insert these 5 documents exactly: {"title": "Book A", "author": "Author 1"}, {"title": "Book B", "author": "Author 2"}, {"title": "Book C", "author": "Author 3"}, {"title": "Book D", "author": "Author 4"}, {"title": "Book E", "author": "Author 5"}.

MongoDB

// Insert the 5 book documents into the books collection
// Your code here

Hint

Use db.books.insertMany([...]) with the exact documents listed.

2

Add pageSize and pageNumber variables

Create two variables: pageSize set to 2, and pageNumber set to 2. These will control how many books to show per page and which page to show.

MongoDB

db.books.insertMany([
  {"title": "Book A", "author": "Author 1"},
  {"title": "Book B", "author": "Author 2"},
  {"title": "Book C", "author": "Author 3"},
  {"title": "Book D", "author": "Author 4"},
  {"title": "Book E", "author": "Author 5"}
])

// Create pageSize and pageNumber variables
// Your code here

Hint

Use const pageSize = 2; and const pageNumber = 2; to create the variables.

3

Write the aggregation pipeline with $skip and $limit

Write a MongoDB aggregation pipeline on books that uses $skip with the value pageSize * (pageNumber - 1) and $limit with the value pageSize.

MongoDB

db.books.insertMany([
  {"title": "Book A", "author": "Author 1"},
  {"title": "Book B", "author": "Author 2"},
  {"title": "Book C", "author": "Author 3"},
  {"title": "Book D", "author": "Author 4"},
  {"title": "Book E", "author": "Author 5"}
])

const pageSize = 2;
const pageNumber = 2;

// Write the aggregation pipeline using $skip and $limit
// Your code here

Hint

Use { $skip: pageSize * (pageNumber - 1) } and { $limit: pageSize } inside an array called pipeline.

4

Run the aggregation pipeline to get the paged books

Run the aggregation pipeline on the books collection using db.books.aggregate(pipeline) and assign the result to a variable called pagedBooks.

MongoDB

db.books.insertMany([
  {"title": "Book A", "author": "Author 1"},
  {"title": "Book B", "author": "Author 2"},
  {"title": "Book C", "author": "Author 3"},
  {"title": "Book D", "author": "Author 4"},
  {"title": "Book E", "author": "Author 5"}
])

const pageSize = 2;
const pageNumber = 2;

const pipeline = [
  { $skip: pageSize * (pageNumber - 1) },
  { $limit: pageSize }
];

// Run the aggregation pipeline and assign to pagedBooks
// Your code here

Hint

Use const pagedBooks = db.books.aggregate(pipeline); to run the pipeline and save the result.

Practice

1. What does the $limit stage do in a MongoDB aggregation pipeline?

easy

A. It skips a number of documents before returning results.

B. It groups documents by a specified field.

C. It sorts the documents in ascending order.

D. It restricts the number of documents returned.

Solution

1. Step 1: Understand the purpose of $limit

   The $limit stage restricts the number of documents that pass through the pipeline to a specified count.

2. Step 2: Compare with other stages

   $skip skips documents, $sort orders them, and $group groups them. Only $limit restricts count.

3. Final Answer:

   It restricts the number of documents returned. -> Option D

4. Quick Check:

   $limit = restrict count [OK]

Hint: Remember: limit = how many results you get [OK]

Common Mistakes:

• Confusing $limit with $skip
• Thinking $limit sorts data
• Mixing $limit with $group

2. Which of the following is the correct syntax to skip 5 documents and then limit the result to 10 documents in a MongoDB aggregation pipeline?

easy

A. [{ $skip: 5 }, { $limit: 10 }]

B. [{ $limit: 10 }, { $skip: 5 }]

C. [{ $skip: 10 }, { $limit: 5 }]

D. [{ $limit: 5 }, { $skip: 10 }]

Solution

1. Step 1: Identify correct order of stages

   To skip first, use $skip then limit results with $limit.

2. Step 2: Match syntax with values

   Skipping 5 then limiting to 10 matches [{ $skip: 5 }, { $limit: 10 }].

3. Final Answer:

   [{ $skip: 5 }, { $limit: 10 }] -> Option A

4. Quick Check:

   Skip first, then limit [OK]

Hint: Skip first, then limit for paging [OK]

Common Mistakes:

• Reversing $limit and $skip order
• Using wrong numbers for skip and limit
• Confusing syntax with find() options

3. Given a collection with documents numbered 1 to 10, what will be the output of this aggregation pipeline?

[{ $skip: 3 }, { $limit: 4 }]

medium

A. [1, 2, 3, 4]

B. [4, 5, 6, 7]

C. [3, 4, 5, 6]

D. [5, 6, 7, 8]

Solution

1. Step 1: Apply $skip: 3 on documents 1 to 10

   Skipping 3 documents removes 1, 2, 3; remaining are 4 to 10.

2. Step 2: Apply $limit: 4 on remaining documents

   Limit to 4 documents returns 4, 5, 6, 7.

3. Final Answer:

   [4, 5, 6, 7] -> Option B

4. Quick Check:

   Skip 3, then take 4 [OK]

Hint: Skip removes first N, limit picks next M [OK]

Common Mistakes:

• Counting skip as inclusive
• Mixing skip and limit values
• Assuming skip resets numbering

4. You wrote this aggregation pipeline but it returns only 2 documents instead of skipping the first 3 from the full collection and limiting to 5:

[{ $limit: 5 }, { $skip: 3 }]

What is the problem?

medium

A. You need to use find() instead of aggregation for skip and limit.

B. The syntax is invalid; $skip cannot be used in aggregation.

C. $skip must come before $limit to work correctly.

D. The pipeline is missing a $match stage before $limit.

Solution

1. Step 1: Understand stage order effect

   $limit first restricts to 5 documents, then $skip tries to skip 3 from those 5.

2. Step 2: Why it returns only 2 documents

   Because $skip after $limit skips from a smaller set (first 5), not the full collection.

3. Final Answer:

   $skip must come before $limit to work correctly. -> Option C

4. Quick Check:

   Skip first, then limit [OK]

Hint: Order matters: skip before limit [OK]

Common Mistakes:

• Placing $limit before $skip
• Thinking $skip is invalid in aggregation
• Confusing aggregation with find()

5. You want to implement pagination on a collection with 100 documents, showing 10 documents per page. Which aggregation pipeline correctly gets the 3rd page of results?

hard

A. [{ $skip: 20 }, { $limit: 10 }]

B. [{ $skip: 30 }, { $limit: 10 }]

C. [{ $limit: 10 }, { $skip: 20 }]

D. [{ $limit: 30 }, { $skip: 10 }]

Solution

1. Step 1: Calculate skip value for page 3

   Each page shows 10 documents, so page 3 skips 2 pages x 10 = 20 documents.

2. Step 2: Apply skip and limit in correct order

   Skip 20 documents, then limit to 10 documents to get page 3 results.

3. Final Answer:

   [{ $skip: 20 }, { $limit: 10 }] -> Option A

4. Quick Check:

   Skip (page-1)*size, then limit size [OK]

Hint: Skip (page-1)*size, then limit size [OK]

Common Mistakes:

• Using wrong skip calculation
• Reversing skip and limit order
• Confusing page number with skip count