Delete with filter conditions in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Delete documents with a specific field value

Given a collection users with documents containing a field status, what will be the result of this delete operation?

MongoDB

db.users.deleteMany({ status: "inactive" })

A Throws an error because the filter condition is invalid.

B Deletes only one document where the status is "inactive" and returns the deleted document.

C Deletes all documents where the status is exactly "inactive" and returns the count of deleted documents.

D Deletes all documents regardless of status and returns the count of deleted documents.

💡 Hint

Remember that deleteMany removes all documents matching the filter.

The deleteMany method deletes all documents matching the filter condition. Here, it deletes all users with status equal to "inactive" and returns the count of deleted documents.

❓ query_result

intermediate

Delete documents with multiple filter conditions

What documents will be deleted by this command?

MongoDB

db.orders.deleteMany({ status: "pending", amount: { $lt: 100 } })

A Deletes all orders with status "pending" and amount less than 100.

B Deletes all orders with status "pending" or amount less than 100.

C Deletes only one order with status "pending" and amount less than 100.

D Deletes all orders regardless of status or amount.

💡 Hint

Multiple conditions inside the filter object are combined with AND logic.

The filter specifies two conditions combined with AND: status must be "pending" AND amount must be less than 100. So only documents matching both are deleted.

📝 Syntax

advanced

Identify the syntax error in delete command

Which option contains a syntax error in the MongoDB delete command?

A db.products.deleteMany({ price: { $gt: 50 } })

B db.products.deleteMany({ price: $gt: 50 })

C db.products.deleteOne({ category: "electronics" })

D db.products.deleteMany({ stock: 0 })

💡 Hint

Check the correct way to write filter conditions with operators.

Option B is invalid because the operator $gt must be inside an object: { price: { $gt: 50 } }. Option B is correct.

❓ optimization

advanced

Optimize deletion of large number of documents

You want to delete millions of documents matching a filter. Which approach is best to avoid performance issues?

A Use <code>deleteMany</code> with the filter directly in one command.

B Use <code>deleteOne</code> repeatedly until all documents are deleted.

C Drop the entire collection and recreate it.

D Delete documents in batches using a loop with <code>deleteMany</code> and a limit on each batch.

💡 Hint

Deleting huge amounts at once can cause locks or timeouts.

Deleting millions of documents at once can cause performance problems. Deleting in batches with limits reduces load and avoids long locks.

🧠 Conceptual

expert

Effect of delete with empty filter

What happens if you run db.collection.deleteMany({})?

MongoDB

db.collection.deleteMany({})

A Deletes all documents in the collection.

B Deletes no documents because the filter is empty.

C Throws an error because the filter cannot be empty.

D Deletes only documents with null fields.

💡 Hint

An empty filter matches all documents.

An empty filter {} matches every document in the collection, so deleteMany({}) deletes all documents.