Pretty printing and cursor behavior in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the pretty() method do in MongoDB?

The pretty() method formats the output of a query to be easier to read by adding indentation and line breaks.

beginner

How does a MongoDB cursor behave when you run a query?

A cursor points to the result set of a query and allows you to iterate over the documents one by one instead of loading all at once.

beginner

What happens if you do not use pretty() on a MongoDB query result?

The output will be shown in a compact JSON format without extra spaces or line breaks, which can be harder to read.

intermediate

How can you retrieve the next document from a MongoDB cursor?

You can use the next() method on the cursor to get the next document in the result set.

intermediate

Why is using a cursor beneficial when working with large datasets in MongoDB?

Because a cursor fetches documents in batches and lets you process them one at a time, it saves memory and improves performance.

What does the pretty() method do in MongoDB?

A Creates a new collection

B Deletes documents from the collection

C Formats query output to be more readable

D Updates documents in the collection

The pretty() method formats the output to add indentation and line breaks for easier reading.

What is a MongoDB cursor?

A A command to delete documents

B A pointer to the result set of a query

C A method to format output

D A type of database index

A cursor points to the query results and allows you to iterate over documents one by one.

Which method retrieves the next document from a MongoDB cursor?

A find()

B insert()

C pretty()

D next()

The next() method returns the next document from the cursor.

What happens if you do not use pretty() on a query result?

A Output is compact JSON without extra spaces

B Query results are deleted

C Cursor is closed automatically

D Output is saved to a file

Without pretty(), the output is shown in compact JSON format which is harder to read.

Why is using a cursor helpful for large datasets?

A It fetches documents in batches to save memory

B It deletes documents faster

C It formats output automatically

D It creates indexes on the fly

Cursors fetch documents in batches, allowing efficient processing without loading all data at once.

Explain how the pretty() method changes the output of a MongoDB query and why it might be useful.

Think about how JSON looks with and without extra spaces.

Describe what a MongoDB cursor is and how it helps when working with query results.

Imagine reading a book page by page instead of all at once.

Practice

1. What does the pretty() method do when used after a MongoDB query?

easy

A. Formats the output to be more readable with indentation and line breaks

B. Limits the number of documents returned by the query

C. Sorts the documents in ascending order

D. Deletes the documents matching the query

Solution

1. Step 1: Understand the purpose of pretty()

   The pretty() method formats the output of a query to make it easier to read by adding indentation and line breaks.

2. Step 2: Compare with other options

   Limiting, sorting, or deleting documents are done by other methods like limit(), sort(), or remove(), not pretty().

3. Final Answer:

   Formats the output to be more readable with indentation and line breaks -> Option A

4. Quick Check:

   pretty() improves readability [OK]

Hint: Remember: pretty() just makes output look nicer [OK]

Common Mistakes:

• Confusing pretty() with limit() or sort()
• Thinking pretty() changes the data
• Assuming pretty() affects query results count

2. Which of the following is the correct syntax to check if a MongoDB cursor has more documents to iterate?

easy

A. cursor.hasMore()

B. cursor.hasNext()

C. cursor.nextExists()

D. cursor.more()

Solution

1. Step 1: Recall cursor methods in MongoDB

   The correct method to check if a cursor has more documents is hasNext().

2. Step 2: Verify other options

   Methods like hasMore(), nextExists(), or more() do not exist in MongoDB cursor API.

3. Final Answer:

   cursor.hasNext() -> Option B

4. Quick Check:

   Use hasNext() to check cursor availability [OK]

Hint: Use hasNext() to check cursor's next document [OK]

Common Mistakes:

• Using non-existent cursor methods
• Confusing hasNext() with next()
• Assuming hasNext() returns the document itself

3. Given the following MongoDB shell commands, what will be the output?

var cursor = db.users.find({age: {$gt: 25}}).pretty();
while(cursor.hasNext()) {
  printjson(cursor.next());
}

medium

A. No output because cursor.next() is missing parentheses

B. Syntax error because pretty() cannot be chained with find()

C. All user documents with age greater than 25 printed in readable JSON format

D. Only the first user document with age greater than 25 printed

Solution

1. Step 1: Analyze the query and cursor usage

   The query finds users with age > 25 and applies pretty() to format output. The while loop uses hasNext() and next() to print each document.

2. Step 2: Understand the output behavior

   Each matching document is printed in readable JSON format until no documents remain.

3. Final Answer:

   All user documents with age greater than 25 printed in readable JSON format -> Option C

4. Quick Check:

   Cursor iterates all matching docs with pretty print [OK]

Hint: pretty() formats output; hasNext() and next() iterate all [OK]

Common Mistakes:

• Thinking pretty() breaks chaining
• Assuming only one document prints
• Forgetting to call next() as a function

4. You run this code in MongoDB shell:

var cursor = db.products.find().pretty();
if(cursor.hasNext) {
  printjson(cursor.next());
}

What is the problem with this code?

medium

A. hasNext is used without parentheses, so it does not check correctly

B. pretty() cannot be used with find()

C. next() should be called before hasNext()

D. printjson() cannot print cursor documents

Solution

1. Step 1: Identify method usage errors

   The method hasNext is used without parentheses, so it refers to the function itself, not its boolean result.

2. Step 2: Understand impact on code behavior

   Because hasNext is not called, the if condition always evaluates to true (function exists), causing unexpected behavior.

3. Final Answer:

   hasNext is used without parentheses, so it does not check correctly -> Option A

4. Quick Check:

   Always call hasNext() with parentheses [OK]

Hint: Call hasNext() with () to get boolean result [OK]

Common Mistakes:

• Using hasNext without parentheses
• Thinking pretty() causes error
• Calling next() before checking hasNext()

5. You want to print all documents from the orders collection where status is "shipped" in a readable format, but only 3 at a time to avoid memory overload. Which code snippet correctly achieves this?

hard

A. var cursor = db.orders.find({status: "shipped"}).batchSize(3); cursor.pretty(); while(cursor.hasNext()) { printjson(cursor.next()); }

B. var cursor = db.orders.find({status: "shipped"}).pretty(); for(var i=0; i<3; i++) { printjson(cursor.next()); }

C. var cursor = db.orders.find({status: "shipped"}).pretty(); while(cursor.hasNext()) { printjson(cursor.next()); if(i==3) break; }

D. var cursor = db.orders.find({status: "shipped"}).limit(3).pretty(); while(cursor.hasNext()) { printjson(cursor.next()); }

Solution

1. Step 1: Limit query results to 3 documents

   Using limit(3) restricts the cursor to only 3 documents matching the filter.

2. Step 2: Use pretty() to format output and iterate with hasNext()/next()

   Chaining pretty() formats output. The while loop prints each document until the 3 limited documents are exhausted.

3. Final Answer:

   var cursor = db.orders.find({status: "shipped"}).limit(3).pretty(); while(cursor.hasNext()) { printjson(cursor.next()); } -> Option D

4. Quick Check:

   limit(3) + pretty() + hasNext()/next() prints 3 formatted docs [OK]

Hint: Use limit(3) before pretty() and iterate with hasNext()/next() [OK]

Common Mistakes:

• Not using limit() to restrict documents
• Calling pretty() after iteration instead of chaining
• Incorrect loop control causing infinite or missing output