Delete all documents in collection in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of deleting all documents using deleteMany({})?

Consider a MongoDB collection named users with 5 documents. What will be the count of documents after running db.users.deleteMany({})?

MongoDB

db.users.deleteMany({})
db.users.countDocuments()

A 0

B 5

C null

D 1

💡 Hint

deleteMany with an empty filter removes all documents.

The deleteMany({}) command deletes all documents in the collection. After deletion, countDocuments() returns 0.

📝 Syntax

intermediate

Which command correctly deletes all documents in a MongoDB collection?

Choose the correct MongoDB command to delete all documents from the orders collection.

A db.orders.remove()

B db.orders.deleteMany({})

C db.orders.deleteAll()

D db.orders.delete({})

💡 Hint

The method deleteMany requires a filter argument.

The correct method to delete all documents is deleteMany with an empty filter object. remove() requires a filter or is deprecated. deleteAll() and delete() do not exist.

❓ optimization

advanced

Which approach is more efficient to remove all documents from a large MongoDB collection?

You want to clear a large collection named logs. Which option is the most efficient?

A db.logs.drop()

B db.logs.deleteMany({})

C db.logs.remove({})

D db.logs.deleteOne({})

💡 Hint

Dropping a collection removes all documents and the collection itself.

Dropping the collection removes all documents and frees storage immediately. deleteMany removes documents but keeps the collection and indexes.

🔧 Debug

advanced

Why does db.products.deleteMany() cause an error?

A developer runs db.products.deleteMany() and gets an error. What is the cause?

MongoDB

db.products.deleteMany()

A Syntax error due to missing semicolon

B deleteMany is not a function

C Collection products does not exist

D Missing filter argument causes a TypeError

💡 Hint

deleteMany requires a filter argument even if empty.

deleteMany requires a filter argument. Calling it without arguments causes a TypeError.

🧠 Conceptual

expert

What happens to indexes when you delete all documents with deleteMany({})?

If you run db.inventory.deleteMany({}) on a collection with indexes, what happens to those indexes?

A Indexes become corrupted and unusable

B All indexes are dropped automatically

C Indexes remain intact and usable

D Indexes are converted to unique constraints

💡 Hint

Deleting documents does not affect the structure of the collection.

deleteMany removes documents but does not drop or alter indexes. Indexes remain intact and ready for new data.