Pretty printing and cursor behavior in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Output of find() with pretty()

What is the output of the following MongoDB query on a collection with documents {"name": "Alice", "age": 30} and {"name": "Bob", "age": 25}?

MongoDB

db.users.find().pretty()

A SyntaxError: pretty() is not a function

B { "name": "Alice", "age": 30 }, { "name": "Bob", "age": 25 }

C [{ "name": "Alice", "age": 30 }, { "name": "Bob", "age": 25 }]

D

{
  "name": "Alice",
  "age": 30
}
{
  "name": "Bob",
  "age": 25
}

💡 Hint

pretty() formats the output with indentation and line breaks.

The pretty() method formats the cursor output to be more readable by adding line breaks and indentation, showing each document on its own lines but not as a JSON array.

🧠 Conceptual

intermediate

Cursor behavior after iteration

After running the following code, what happens if you try to iterate over the cursor again?

MongoDB

var cursor = db.users.find();
while(cursor.hasNext()) {
  printjson(cursor.next());
}
// Now iterate again
while(cursor.hasNext()) {
  printjson(cursor.next());
}

A The second loop resets the cursor automatically and prints all documents.

B The second loop prints no documents because the cursor is exhausted.

C The second loop throws a runtime error because the cursor is closed.

D The second loop prints the same documents again.

💡 Hint

Think about how cursors work in MongoDB after reading all documents.

Once a cursor is fully iterated, it is exhausted and has no more documents to return. You cannot iterate over it again without creating a new cursor.

📝 Syntax

advanced

Correct usage of pretty() with find()

Which of the following MongoDB shell commands correctly uses pretty() to format the output of a find query?

A db.collection.find().pretty

B db.collection.pretty().find()

C db.collection.find().pretty()

D db.collection.find(pretty())

💡 Hint

pretty() is a method called on the cursor returned by find().

pretty() is a method chained after find() to format the output. Calling pretty() before find() or passing it as an argument is invalid syntax.

❓ optimization

advanced

Improving performance when pretty printing large query results

You want to pretty print a large number of documents from a collection. Which approach is best to avoid performance issues?

A Use find().limit(10).pretty() to print only a small number of documents.

B Use find().pretty() with no limit and print all documents at once.

C Use find().pretty() and store all results in an array before printing.

D Use find() without pretty() and format the output manually in the application.

💡 Hint

Consider how much data is processed and displayed at once.

Limiting the number of documents reduces memory and processing load, making pretty printing faster and more responsive for large datasets.

🔧 Debug

expert

Diagnosing cursor error after pretty() usage

You run this code in the MongoDB shell: var cursor = db.users.find().pretty(); printjson(cursor.next()); printjson(cursor.next()); But you get an error: "TypeError: cursor.next is not a function". What is the cause?

A pretty() returns a string, not a cursor, so next() is undefined.

B The cursor is exhausted after the first next() call, so the second fails.

C The find() method must be called with a query object to use next().

D The pretty() method must be called after next(), not before.

💡 Hint

Check what pretty() returns compared to find().

pretty() formats the output as a string and does not return a cursor. Calling next() on the string causes a TypeError.