Pretty printing and cursor behavior in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to pretty print all documents from the 'users' collection.

MongoDB

db.users.find().[1]()

Drag options to blanks, or click blank then click option'

Apretty

BtoArray

Ccount

Dlimit

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'toArray()' instead of 'pretty()' which returns an array but does not format output.

Using 'count()' which returns the number of documents, not the documents themselves.

The 'pretty()' method formats the output for easier reading in the MongoDB shell.

2fill in blank

medium

Complete the code to get the first 5 documents from the 'orders' collection.

MongoDB

db.orders.find().[1](5)

Drag options to blanks, or click blank then click option'

Askip

Bpretty

Climit

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'skip()' which skips documents but does not limit the number returned.

Using 'count()' which returns the number of documents, not the documents themselves.

The 'limit()' method restricts the number of documents returned by the query.

3fill in blank

hard

Fix the error in the code to convert the cursor to an array.

MongoDB

const docs = db.products.find().[1]()

Drag options to blanks, or click blank then click option'

AtoArray

Bpretty

Ccount

Dlimit

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pretty()' which formats output but does not convert to array.

Using 'count()' which returns the number of documents.

The 'toArray()' method converts the cursor to an array of documents.

4fill in blank

hard

Fill both blanks to skip the first 3 documents and limit the result to 4 documents.

MongoDB

db.sales.find().[1](3).[2](4)

Drag options to blanks, or click blank then click option'

Askip

Blimit

Cpretty

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Reversing the order of 'skip' and 'limit' which changes the result.

Using 'pretty' or 'count' which do not control skipping or limiting.

The 'skip()' method skips documents, and 'limit()' restricts the number returned.

5fill in blank

hard

Fill all three blanks to pretty print documents from 'inventory', skip 2, and limit to 3.

MongoDB

db.inventory.find().[1]().[2](2).[3](3)

Drag options to blanks, or click blank then click option'

Apretty

Bskip

Climit

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'count()' which does not affect output formatting or cursor behavior.

Changing the order of methods which affects the result.

Use 'pretty()' to format output, 'skip()' to skip documents, and 'limit()' to restrict the number returned.

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