insertMany method in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this insertMany operation?

Consider a MongoDB collection named students. You run the following command:

db.students.insertMany([
  { name: "Alice", age: 20 },
  { name: "Bob", age: 22 }
])

What does the insertMany method return?

MongoDB

db.students.insertMany([{ name: "Alice", age: 20 }, { name: "Bob", age: 22 }])

A {"acknowledged": true, "insertedCount": 2, "insertedIds": {"0": ObjectId(...), "1": ObjectId(...)}}

B {"acknowledged": false, "insertedCount": 0, "insertedIds": {}}

C An error because insertMany only accepts one document

D {"acknowledged": true, "insertedCount": 1, "insertedIds": {"0": ObjectId(...)}}

💡 Hint

insertMany inserts multiple documents and returns info about all inserted documents.

The insertMany method inserts all documents in the array and returns an object showing it succeeded (acknowledged: true), how many documents were inserted (insertedCount), and the IDs of inserted documents (insertedIds).

📝 Syntax

intermediate

Which option is a correct syntax for insertMany?

Which of the following is the correct syntax to insert multiple documents into a MongoDB collection orders using insertMany?

A db.orders.insertMany({ item: "book", qty: 5 }, { item: "pen", qty: 10 })

B db.orders.insertMany([{ item: "book", qty: 5 }, { item: "pen", qty: 10 }])

C db.orders.insertMany([{ item: "book", qty: 5 }], [{ item: "pen", qty: 10 }])

D db.orders.insertMany(item: "book", qty: 5, item: "pen", qty: 10)

💡 Hint

insertMany expects a single array of documents as its argument.

The insertMany method requires one array containing all documents to insert. Option B correctly passes an array of two documents.

❓ optimization

advanced

Why use insertMany instead of multiple insertOne calls?

You want to add 1000 new user documents to a MongoDB collection. Which is the best reason to use insertMany instead of calling insertOne 1000 times?

A insertMany sends all documents in one request, reducing network overhead and improving performance.

B insertMany validates documents more strictly than insertOne.

C insertMany automatically creates indexes for the documents.

D insertMany can only insert documents with the same fields.

💡 Hint

Think about how many times the database is contacted.

Using insertMany sends all documents in a single request, which reduces the number of network round-trips and speeds up the insertion process compared to calling insertOne repeatedly.

🔧 Debug

advanced

What error occurs with this insertMany call?

Given the following code:

db.products.insertMany([
  { name: "Table", price: 100 },
  { name: "Chair" price: 50 }
])

What error will MongoDB raise?

A No error, documents inserted successfully

B DuplicateKeyError because of repeated document fields

C TypeError because insertMany expects an object, not an array

D SyntaxError due to missing comma between fields in second document

💡 Hint

Look carefully at the second document's fields.

The second document is missing a comma between "Chair" and price: 50, causing a syntax error in the JavaScript object.

🧠 Conceptual

expert

What happens if insertMany is called with an empty array?

What is the result of running db.collection.insertMany([]) in MongoDB?

A Returns null without any acknowledgment

B Throws an error because the array is empty

C Returns acknowledged true with insertedCount 0 and empty insertedIds

D Inserts a single empty document into the collection

💡 Hint

Think about what happens when you insert zero documents.

Calling insertMany with an empty array returns an acknowledgment with zero documents inserted and an empty insertedIds object. It does not throw an error or insert anything.