countDocuments method in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the countDocuments() method do in MongoDB?

It counts the number of documents in a collection that match a given filter or query.

beginner

How do you count all documents in a collection using countDocuments()?

Call countDocuments({}) with an empty filter object to count all documents.

intermediate

What is the difference between count() and countDocuments() in MongoDB?

countDocuments() counts documents matching a filter accurately, while count() is deprecated and less precise with some query types.

beginner

Write a simple example to count documents where the field status equals "active".

db.collection.countDocuments({ status: "active" })

intermediate

Can countDocuments() be used with complex filters like ranges or logical operators?

Yes, you can use any valid MongoDB query filter with countDocuments(), including ranges, $and, $or, and others.

What does countDocuments({}) return?

A The number of fields in a document

B The number of collections in the database

C The total number of documents in the collection

D The size of the database in bytes

countDocuments({}) counts all documents in the collection because the filter is empty.

Which method is recommended for counting documents in MongoDB?

A countDocuments()

B count()

C find()

D aggregate()

countDocuments() is the recommended method for accurate document counts.

What type of argument does countDocuments() accept?

A A query filter object

B A string with collection name

C A number representing limit

D No arguments allowed

countDocuments() takes a query filter object to specify which documents to count.

If you want to count documents where age is greater than 30, which filter is correct?

A { age: 30 }

B { age: { $gt: 30 } }

C { age: { $lt: 30 } }

D { age: { $eq: 30 } }

The $gt operator means 'greater than', so { age: { $gt: 30 } } counts documents with age over 30.

What does countDocuments({ status: "active" }) return?

A Number of documents with any status

B Number of fields named 'status'

C Number of collections named 'active'

D Number of documents with status 'active'

This counts only documents where the status field equals 'active'.

Explain how to use the countDocuments() method to find the number of documents matching a condition.

Think about how you tell MongoDB what to count.

Describe the difference between countDocuments() and the deprecated count() method.

Focus on why one is preferred over the other.