deleteOne method in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this deleteOne operation?

Consider a MongoDB collection named users with documents:

{ "_id": 1, "name": "Alice" }

{ "_id": 2, "name": "Bob" }

What will be the result of this command?

db.users.deleteOne({ name: "Alice" })

MongoDB

db.users.deleteOne({ name: "Alice" })

A {"acknowledged": true, "deletedCount": 1}

B {"acknowledged": true, "deletedCount": 0}

C SyntaxError: missing parentheses

D TypeError: deleteOne is not a function

💡 Hint

deleteOne removes the first document matching the filter.

The deleteOne method deletes one document matching the filter. Since a document with name 'Alice' exists, deletedCount is 1.

🧠 Conceptual

intermediate

Which statement about deleteOne is true?

Choose the correct statement about the MongoDB deleteOne method.

A deleteOne deletes exactly one document matching the filter.

B deleteOne deletes all documents matching the filter.

C deleteOne returns the deleted document.

D deleteOne requires the document _id to delete.

💡 Hint

Think about how many documents deleteOne removes.

deleteOne deletes only the first document that matches the filter. It does not delete all matching documents or return the deleted document.

📝 Syntax

advanced

Which deleteOne command is syntactically correct?

Identify the correct syntax for deleting one document where age is 30.

A db.collection.deleteOne[ { age: 30 } ]

B db.collection.deleteOne({ age: 30 })

C db.collection.deleteOne({age:30}

D db.collection.deleteOne(age == 30)

💡 Hint

deleteOne takes a filter object inside parentheses.

Option B uses correct syntax: method call with a filter object inside parentheses. Others have syntax errors.

🔧 Debug

advanced

Why does this deleteOne command fail?

Given the command:

db.users.deleteOne({ "name": "Charlie" })

and the error:

TypeError: db.users.deleteOne is not a function

What is the most likely cause?

A The filter object is missing required fields.

B The deleteOne method is misspelled.

C The database connection is not established properly.

D The collection name is incorrect or does not exist.

💡 Hint

Verify the database connection and collection reference.

The TypeError indicates that db.users does not have deleteOne as a function, which typically occurs when the database connection is not established properly or the shell/context is incorrect.

❓ optimization

expert

How to optimize deleting a document by _id using deleteOne?

You want to delete a document by its unique _id field efficiently. Which option is the best practice?

A db.collection.deleteOne({ _id: new ObjectId("507f1f77bcf86cd799439011") })

B db.collection.deleteOne({ _id: "507f1f77bcf86cd799439011" })

C db.collection.deleteOne({ id: ObjectId("507f1f77bcf86cd799439011") })

D db.collection.deleteOne({ _id: ObjectId("507f1f77bcf86cd799439011") })

💡 Hint

The _id field is an ObjectId type, not a string.

The _id field must be matched with an ObjectId instance. Option D uses ObjectId correctly. Option D uses a string, which won't match. Option D uses wrong field name. Option D uses new ObjectId which is not standard in shell.