deleteMany method in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the deleteMany() method do in MongoDB?

It removes all documents from a collection that match a given filter condition.

beginner

How do you specify which documents to delete using deleteMany()?

You provide a filter object that describes the criteria documents must meet to be deleted.

intermediate

What does deleteMany({}) do?

It deletes all documents in the collection because the empty filter matches everything.

intermediate

What is the return value of deleteMany()?

It returns a result object containing the number of documents deleted, accessible via deletedCount.

beginner

Why should you be careful when using deleteMany() without a filter?

Because it will delete all documents in the collection, which might cause data loss if unintended.

What does deleteMany({ age: { $lt: 18 } }) do?

A Deletes all documents where age is less than 18

B Deletes all documents where age is greater than 18

C Deletes all documents regardless of age

D Deletes no documents

The filter { age: { $lt: 18 } } matches documents with age less than 18, so those are deleted.

What will happen if you call deleteMany({}) on a collection?

A Deletes no documents

B Deletes documents with null values

C Deletes all documents

D Throws an error

An empty filter matches all documents, so all documents are deleted.

Which property tells you how many documents were deleted after deleteMany()?

A deletedCount

B countDeleted

C deletedDocuments

D deleteCount

The result object from deleteMany() includes a property called deletedCount showing how many documents were removed.

If you want to delete documents where the field 'status' equals 'inactive', what filter should you use?

A {}

B { status: { $eq: 'active' } }

C { inactive: true }

D { status: 'inactive' }

The filter { status: 'inactive' } matches documents where status is exactly 'inactive'.

Is it possible to delete documents using deleteMany() without specifying a filter?

A No, filter is required

B Yes, it deletes all documents

C Yes, but it deletes none

D No, it throws an error

Calling deleteMany() with an empty filter deletes all documents in the collection.

Explain how the deleteMany() method works in MongoDB and what happens if you use an empty filter.

Think about how you tell MongoDB which documents to remove.

Describe the importance of the deletedCount property after calling deleteMany().

Consider how you know if your delete worked.