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.

Practice

1. What does the insertMany method do in MongoDB?

easy

A. Finds multiple documents in a collection

B. Deletes multiple documents from a collection

C. Updates multiple documents in a collection

D. Inserts multiple documents into a collection at once

Solution

1. Step 1: Understand the purpose of insertMany

   The insertMany method is designed to add several documents to a MongoDB collection in a single operation.

2. Step 2: Compare with other operations

   Unlike delete, update, or find, insertMany specifically inserts new documents.

3. Final Answer:

   Inserts multiple documents into a collection at once -> Option D

4. Quick Check:

   insertMany = Insert multiple documents [OK]

Hint: Remember: insertMany means insert many documents at once [OK]

Common Mistakes:

• Confusing insertMany with update or delete methods
• Thinking insertMany finds documents
• Assuming insertMany inserts only one document

2. Which of the following is the correct syntax to insert multiple documents using insertMany in MongoDB?

easy

A. db.collection.insertMany('Alice', 'Bob')

B. db.collection.insertMany({name: 'Alice', name: 'Bob'})

C. db.collection.insertMany([{name: 'Alice'}, {name: 'Bob'}])

D. db.collection.insertMany([{name: 'Alice'}], [{name: 'Bob'}])

Solution

1. Step 1: Check the parameter type for insertMany

   insertMany expects an array of documents (objects) inside square brackets.

2. Step 2: Validate each option's syntax

   db.collection.insertMany([{name: 'Alice'}, {name: 'Bob'}]) correctly passes an array of two objects. Options B, C, and D have incorrect formats: B uses an object instead of array, C passes strings, D passes two arrays separately.

3. Final Answer:

   db.collection.insertMany([{name: 'Alice'}, {name: 'Bob'}]) -> Option C

4. Quick Check:

   Array of documents = Correct syntax [OK]

Hint: Use an array of objects inside insertMany brackets [OK]

Common Mistakes:

• Passing a single object instead of an array
• Passing multiple arrays instead of one array
• Passing strings instead of objects

3. What will be the result of this code snippet?

db.users.insertMany([
  {name: 'John', age: 25},
  {name: 'Jane', age: 30}
])

medium

A. Two new documents will be added to the 'users' collection

B. An error will occur because age is missing in one document

C. Only the first document will be inserted

D. The collection will be deleted

Solution

1. Step 1: Analyze the documents passed to insertMany

   Both documents have valid fields: name and age. There is no missing required field indicated.

2. Step 2: Understand insertMany behavior

   By default, insertMany inserts all documents in the array into the collection.

3. Final Answer:

   Two new documents will be added to the 'users' collection -> Option A

4. Quick Check:

   Valid array of documents = Insert all [OK]

Hint: Valid documents array inserts all documents [OK]

Common Mistakes:

• Assuming missing fields cause errors without schema
• Thinking only one document inserts by default
• Confusing insertMany with delete or update

4. Identify the error in this insertMany usage:

db.products.insertMany(
  {name: 'Pen', price: 1.5},
  {name: 'Pencil', price: 0.5}
)

medium

A. Missing array brackets around documents

B. Incorrect method name, should be insertOne

C. Documents have invalid field names

D. No error, code is correct

Solution

1. Step 1: Check the parameter passed to insertMany

   insertMany requires a single array containing all documents, but here two separate objects are passed without array brackets.

2. Step 2: Understand correct syntax

   The correct syntax wraps documents inside square brackets: [{...}, {...}].

3. Final Answer:

   Missing array brackets around documents -> Option A

4. Quick Check:

   Documents must be in an array [OK]

Hint: Always wrap documents in an array for insertMany [OK]

Common Mistakes:

• Passing multiple objects without array
• Using insertOne for multiple documents
• Assuming field names cause syntax errors

5. You want to insert multiple documents but continue inserting even if one document fails. Which option should you use with insertMany?

hard

A. { ordered: true }

B. { ordered: false }

C. { continueOnError: true }

D. { ignoreErrors: true }

Solution

1. Step 1: Understand the ordered option in insertMany

   By default, ordered is true, meaning insertion stops on first error. Setting it to false allows continuing inserts despite errors.

2. Step 2: Evaluate the options

   { ordered: false } correctly sets ordered: false. Options A, B, and D are incorrect: A stops on error, B and D use invalid options.

3. Final Answer:

   { ordered: false } -> Option B

4. Quick Check:

   ordered: false = Continue on error [OK]

Hint: Use ordered: false to continue inserts after errors [OK]

Common Mistakes:

• Using ordered: true which stops on first error
• Using non-existent options like continueOnError
• Confusing error handling options