estimatedDocumentCount for speed in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the estimated number of documents in the collection.

MongoDB

const count = await collection.[1]();

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

AestimatedDocumentCount

BcountDocuments

Cfind

Daggregate

Attempts:

3 left

💡 Hint

Common Mistakes

Using countDocuments() which is slower because it scans documents.

Using find() which returns documents, not a count.

Using aggregate() which is for complex queries.

The estimatedDocumentCount() method quickly returns an estimate of the total number of documents in a collection without scanning the entire collection.

2fill in blank

medium

Complete the code to print the estimated document count from the collection.

MongoDB

collection.[1]().then(count => console.log(count));

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

AcountDocuments

Bfind

CestimatedDocumentCount

DdeleteMany

Attempts:

3 left

💡 Hint

Common Mistakes

Using deleteMany() which deletes documents instead of counting.

Using find() which returns documents, not a count.

Using countDocuments() which is slower.

estimatedDocumentCount() returns a promise that resolves to the estimated number of documents, which we print.

3fill in blank

hard

Fix the error in the code to get the estimated document count correctly.

MongoDB

const count = await collection.[1];

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

AestimatedDocumentCount

BestimatedDocumentCount()

CcountDocuments()

DcountDocuments

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting parentheses after the method name.

Using countDocuments() which is slower.

Using property without calling it as a function.

The method estimatedDocumentCount() must be called with parentheses to execute and return a promise.

4fill in blank

hard

Fill both blanks to estimate the document count and handle errors.

MongoDB

collection.[1]().catch(error => console.[2](error));

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

AestimatedDocumentCount

Berror

Cerror.log

Dconsole.error

Attempts:

3 left

💡 Hint

Common Mistakes

Using console.log instead of console.error for errors.

Using countDocuments instead of estimatedDocumentCount.

Using error.log which is not a function.

Use estimatedDocumentCount() to get the count and console.error to print errors.

5fill in blank

hard

Fill all three blanks to estimate document count, assign it to a variable, and print it.

MongoDB

async function getCount() {
  const count = await collection.[1]();
  console.[2]('Estimated count:', [3]);
}

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

AestimatedDocumentCount

Blog

Ccount

DcountDocuments

Attempts:

3 left

💡 Hint

Common Mistakes

Using countDocuments instead of estimatedDocumentCount.

Using console.error instead of console.log for printing count.

Printing the method name instead of the variable.

Call estimatedDocumentCount() to get the count, then use console.log to print the variable count.

Practice

1. What does the estimatedDocumentCount() method in MongoDB do?

easy

A. Updates documents in a collection

B. Returns a fast, approximate count of all documents in a collection

C. Deletes documents from a collection

D. Returns the exact count of documents matching a filter

Solution

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

   This method provides a quick estimate of the total number of documents in a collection without scanning all documents.

2. Step 2: Compare with other count methods

   Unlike countDocuments(), it does not accept filters and is faster but less precise.

3. Final Answer:

   Returns a fast, approximate count of all documents in a collection -> Option B

4. Quick Check:

   estimatedDocumentCount() = approximate total count [OK]

Hint: estimatedDocumentCount() gives fast total count without filters [OK]

Common Mistakes:

• Thinking it accepts filters like countDocuments()
• Confusing it with update or delete operations
• Expecting exact counts always

2. Which of the following is the correct syntax to get an estimated count of documents in a MongoDB collection named users?

easy

A. db.users.count()

B. db.users.countDocuments()

C. db.users.estimatedCount()

D. db.users.estimatedDocumentCount()

Solution

1. Step 1: Recall the exact method name

   The method to get an estimated count is estimatedDocumentCount(), called on the collection object.

2. Step 2: Verify syntax correctness

   db.users.estimatedDocumentCount() uses the correct method and syntax: db.users.estimatedDocumentCount().

3. Final Answer:

   db.users.estimatedDocumentCount() -> Option D

4. Quick Check:

   Correct method name and syntax = db.users.estimatedDocumentCount() [OK]

Hint: Use exact method name estimatedDocumentCount() on collection [OK]

Common Mistakes:

• Using countDocuments() which is exact, not estimated
• Using non-existent method estimatedCount()
• Using deprecated count() method

3. Given a collection orders with 1000 documents, what will db.orders.estimatedDocumentCount() most likely return?

medium

A. A fast approximate number close to 1000

B. Exactly 1000

C. 0

D. An error because filters are missing

Solution

1. Step 1: Understand the behavior of estimatedDocumentCount()

   This method returns a fast estimate, which may not be exactly the number of documents but close to it.

2. Step 2: Analyze the expected output

   Since the collection has 1000 documents, the method will return a number near 1000 quickly, not necessarily exactly 1000.

3. Final Answer:

   A fast approximate number close to 1000 -> Option A

4. Quick Check:

   estimatedDocumentCount() ≈ actual count [OK]

Hint: estimatedDocumentCount() returns approximate count, not exact [OK]

Common Mistakes:

• Expecting exact count always
• Thinking it returns zero without filters
• Assuming it throws error without filters

4. What is wrong with this code snippet?

const count = db.products.estimatedDocumentCount({ category: 'books' });

medium

A. The collection name is incorrect

B. The method name is misspelled

C. estimatedDocumentCount() does not accept any filter arguments

D. estimatedDocumentCount() requires a callback function

Solution

1. Step 1: Check method argument rules

   The estimatedDocumentCount() method does not accept any filter or query arguments.

2. Step 2: Identify the error in the code

   Passing { category: 'books' } as an argument is invalid and will cause an error.

3. Final Answer:

   estimatedDocumentCount() does not accept any filter arguments -> Option C

4. Quick Check:

   No filters allowed in estimatedDocumentCount() [OK]

Hint: estimatedDocumentCount() takes no arguments, no filters allowed [OK]

Common Mistakes:

• Passing filter objects to estimatedDocumentCount()
• Assuming it works like countDocuments()
• Expecting a callback is mandatory

5. You want to quickly display the total number of documents in a large logs collection for a dashboard, but exact precision is not critical. Which method should you use and why?

hard

A. Use estimatedDocumentCount() for fast approximate count without filters

B. Use countDocuments({}) for exact count with no filters

C. Use find().count() to count documents with a query

D. Use aggregate([{ $count: 'total' }]) for counting

Solution

1. Step 1: Identify the requirement for speed over precision

   The question states speed is important and exact precision is not critical.

2. Step 2: Choose the method that fits speed and approximate count

   estimatedDocumentCount() provides a fast, approximate count without filters, ideal for large collections and dashboards.

3. Final Answer:

   Use estimatedDocumentCount() for fast approximate count without filters -> Option A

4. Quick Check:

   Fast approximate count = estimatedDocumentCount() [OK]

Hint: For fast total count without exactness, use estimatedDocumentCount() [OK]

Common Mistakes:

• Choosing exact count methods that are slower
• Using deprecated or inefficient counting methods
• Trying to filter with estimatedDocumentCount()