insertOne method in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this insertOne operation?

Consider the following MongoDB insertOne command. What will be the output after running it?

MongoDB

db.users.insertOne({name: "Alice", age: 30})

A SyntaxError: missing parentheses in call to 'insertOne'

B {"acknowledged": false, "insertedId": null}

C {"acknowledged": true, "insertedId": ObjectId("some_id")}

D TypeError: insertOne is not a function

💡 Hint

insertOne returns an object with acknowledged true and the inserted document's id.

The insertOne method returns an object confirming the insertion with acknowledged set to true and the insertedId containing the new document's unique ObjectId.

📝 Syntax

intermediate

Which option has the correct syntax to insert a document with insertOne?

Choose the option that correctly uses insertOne to add a document with fields name and age.

A db.collection.insertOne(name: "Bob", age: 25)

B db.collection.insertOne({name: "Bob", age: 25})

C db.collection.insertOne(["name": "Bob", "age": 25])

D db.collection.insertOne({"name" = "Bob", "age" = 25})

💡 Hint

insertOne expects a single document object inside curly braces.

The correct syntax uses curly braces with key-value pairs separated by colons inside insertOne. Other options have syntax errors like missing braces or wrong separators.

❓ optimization

advanced

Which insertOne usage is best to ensure the document has a unique email field?

You want to insert a user document but avoid duplicates on the email field. Which option helps achieve this?

A db.users.insertOne({name: "Eve", email: "[e-mail]"})

B db.users.insertOne({name: "Eve", email: "[e-mail]"}, {unique: true})

C db.users.insertOne({name: "Eve", email: "[e-mail]"}, {upsert: true})

D db.users.createIndex({email: 1}, {unique: true}); db.users.insertOne({name: "Eve", email: "[e-mail]"})

💡 Hint

Unique constraints are set by indexes, not by insertOne options.

To ensure uniqueness on a field, create a unique index on that field before inserting. insertOne alone does not enforce uniqueness.

🔧 Debug

advanced

Why does this insertOne command fail with a TypeError?

Given the code: db.users.insertOne([{"name": "John"}]) Why does it raise a TypeError?

MongoDB

db.users.insertOne([{"name": "John"}])

A Because insertOne expects a single document object, not an array.

B Because the document is missing a required _id field.

C Because the collection 'users' does not exist.

D Because the name field must be a string, not an object.

💡 Hint

insertOne accepts one document, not an array of documents.

insertOne requires a single document object. Passing an array causes a TypeError because the method cannot handle arrays.

🧠 Conceptual

expert

What happens if you call insertOne with a document missing the _id field?

In MongoDB, if you run insertOne({name: "Sam"}) without specifying _id, what will the database do?

A MongoDB automatically generates a unique ObjectId for the _id field.

B The insertOne operation fails with a missing _id error.

C The document is inserted with _id set to null.

D MongoDB assigns the _id field the value of the name field.

💡 Hint

MongoDB always requires a unique _id for each document.

If _id is not provided, MongoDB creates a unique ObjectId automatically to ensure each document has a unique identifier.