Drop collection vs deleteMany in MongoDB - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Difference in effect between drop() and deleteMany()

What is the main difference between using db.collection.drop() and db.collection.deleteMany({}) in MongoDB?

A drop() only deletes documents matching a filter, deleteMany({}) deletes the entire collection.

B drop() and deleteMany({}) both remove all documents but keep the collection structure intact.

C drop() removes the entire collection including indexes, while deleteMany({}) removes all documents but keeps the collection and indexes.

D drop() removes documents one by one, deleteMany({}) removes the collection instantly.

💡 Hint

Think about what happens to the collection itself after each operation.

drop() deletes the entire collection and its indexes from the database. deleteMany({}) deletes all documents but leaves the collection and its indexes intact.

❓ query_result

intermediate

Result of drop() on a non-existent collection

What is the result of running db.nonexistent.drop() if the collection does not exist?

A Returns false and does not throw an error.

B Throws an error indicating the collection does not exist.

C Creates the collection and then drops it, returning true.

D Returns true even though the collection did not exist.

💡 Hint

Consider if drop() requires the collection to exist to succeed.

Calling drop() on a non-existent collection returns false and does not throw an error.

📝 Syntax

advanced

Correct syntax to delete all documents in a collection

Which of the following MongoDB commands correctly deletes all documents from the users collection without dropping it?

A db.users.deleteMany({})

B db.users.drop()

C db.users.remove()

D db.users.delete()

💡 Hint

Remember the modern method to delete multiple documents.

deleteMany({}) deletes all documents matching the empty filter, effectively deleting all documents but keeping the collection.

drop() removes the entire collection. remove() is deprecated. delete() is not a valid method.

❓ optimization

advanced

Performance difference between drop() and deleteMany({})

Which statement best describes the performance difference when removing all data from a large collection?

A Both have the same performance because they remove all data.

B drop() is faster because it removes the entire collection and indexes immediately, while deleteMany({}) deletes documents one by one.

C deleteMany({}) is faster because it uses bulk operations internally, drop() is slower due to index rebuilding.

D drop() is slower because it requires recreating the collection manually after.

💡 Hint

Think about what happens internally when a collection is dropped versus documents deleted.

drop() quickly removes the entire collection and all indexes, which is faster than deleting documents individually with deleteMany({}).

🔧 Debug

expert

Unexpected behavior after drop() and insert

After running db.orders.drop() and then inserting a document into orders, what is the state of the collection?

MongoDB

db.orders.drop()
db.orders.insertOne({item: 'book', qty: 3})
db.orders.getIndexes()

A The insertOne() fails because the collection was dropped.

B The collection does not exist because drop() permanently deletes it.

C The collection exists with the inserted document and all previous indexes restored.

D The collection exists with the inserted document but has only the default _id index.

💡 Hint

Consider what happens to indexes after dropping and recreating a collection.

After dropping a collection, all indexes are removed. Inserting a document recreates the collection with only the default _id index.