skip method for offset in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Using skip() to offset results

Given a MongoDB collection students with documents sorted by score in descending order, what will be the output of the following query?

db.students.find().sort({score: -1}).skip(3).limit(2)

Assume the collection has 6 documents with scores: 95, 90, 85, 80, 75, 70.

MongoDB

db.students.find().sort({score: -1}).skip(3).limit(2)

A Documents with scores 80 and 75

B Documents with scores 85 and 80

C Documents with scores 75 and 70

D Documents with scores 90 and 85

💡 Hint

Remember that skip(3) skips the first 3 documents after sorting.

The query sorts documents by score descending: 95, 90, 85, 80, 75, 70. Then it skips the first 3 (95, 90, 85), so the next documents are 80 and 75, which are returned by limit(2).

🧠 Conceptual

intermediate

Purpose of skip() in MongoDB queries

What is the main purpose of the skip() method in MongoDB queries?

A To skip a specified number of documents in the result set, useful for pagination

B To remove documents from the collection permanently

C To skip documents that do not match the query filter

D To skip the execution of the query entirely

💡 Hint

Think about how you would show page 2 of results after page 1.

The skip() method skips a specified number of documents in the query result, allowing you to offset results for pagination or other purposes.

📝 Syntax

advanced

Correct syntax for skip() usage

Which of the following MongoDB queries correctly uses the skip() method to skip 5 documents?

A db.collection.find().skip()

B db.collection.skip(5).find()

C db.collection.find().skip(5)

D db.collection.find().skip = 5

💡 Hint

skip() is a method chained after find(), not a property or called before find().

The correct syntax is to call skip() as a method after find(), passing the number of documents to skip as an argument.

❓ optimization

advanced

Performance considerations when using skip()

Why can using skip() with a large offset value cause performance issues in MongoDB?

A Because skip() locks the entire collection during execution

B Because skip() deletes the skipped documents causing overhead

C Because skip() causes the query to run without using indexes

D Because MongoDB must scan and discard all skipped documents before returning results

💡 Hint

Think about what MongoDB does internally when skipping documents.

MongoDB still scans the skipped documents internally, which can be slow for large skip values because it must process and discard those documents before returning the requested results.

🔧 Debug

expert

Identifying error in skip() usage

Consider the following MongoDB query:

db.orders.find().skip(-3)

What error will this query produce?

A SyntaxError: Unexpected token '-'

B MongoError: skip value must be non-negative

C No error, query returns all documents

D TypeError: skip() expects a string argument

💡 Hint

skip() expects a positive number or zero.

The skip() method requires a non-negative integer. Passing a negative number causes a MongoError indicating the skip value must be non-negative.