Why updating documents matters in MongoDB - Challenge Your Understanding

Challenge - 5 Problems

❓ query_result

intermediate

What is the output after updating a document?

Consider a MongoDB collection users with a document:

{ "name": "Alice", "age": 25 }

We run this update query:

db.users.updateOne({ "name": "Alice" }, { $set: { "age": 26 } })

What will be the value of age for Alice after this update?

MongoDB

db.users.updateOne({ "name": "Alice" }, { $set: { "age": 26 } })
db.users.find({ "name": "Alice" }).toArray()

A {"name": "Alice", "age": 25}

B {"name": "Alice"}

C No document found

D {"name": "Alice", "age": 26}

💡 Hint

Think about what $set does in an update operation.

The $set operator changes the value of the specified field. Here, it updates age from 25 to 26.

🧠 Conceptual

intermediate

Why is updating documents important in databases?

Why do we need to update documents in a database like MongoDB?

A To add new documents only

B To change existing data without deleting and recreating documents

C To delete all documents in a collection

D To create indexes automatically

💡 Hint

Think about how data changes over time.

Updating documents allows us to modify existing data efficiently without removing and adding new documents, which keeps data consistent and operations faster.

📝 Syntax

advanced

Which update query correctly increments a field?

Given a document { "name": "Bob", "score": 10 }, which MongoDB update query correctly increases score by 5?

A db.users.updateOne({ "name": "Bob" }, { $inc: { "score": 5 } })

B db.users.updateOne({ "name": "Bob" }, { $set: { "score": "score + 5" } })

C db.users.updateOne({ "name": "Bob" }, { $add: { "score": 5 } })

D db.users.updateOne({ "name": "Bob" }, { $increase: { "score": 5 } })

💡 Hint

Look for the operator that increments numeric fields.

The $inc operator increments the value of a field by the specified amount. Other options are invalid operators or incorrect syntax.

🔧 Debug

advanced

Why does this update query fail?

Consider this update query:

db.products.updateOne({ "id": 101 }, { "price": 19.99 })

Why will it replace the entire document instead of just updating the price field?

A Because the update document is missing an update operator like $set

B Because the query filter is incorrect

C Because the collection name is wrong

D Because the price value is not a string

💡 Hint

Check the structure of the update document.

When no update operator like $set is used, MongoDB replaces the entire document with the update document. Use $set to update only specific fields.

❓ optimization

expert

How to efficiently update multiple documents?

You want to increase the stock field by 10 for all products with category "books". Which query is the most efficient?

A db.products.updateOne({ "category": "books" }, { $inc: { "stock": 10 } })

B db.products.find({ "category": "books" }).forEach(doc => { db.products.updateOne({ _id: doc._id }, { $inc: { "stock": 10 } }) })

C db.products.updateMany({ "category": "books" }, { $inc: { "stock": 10 } })

D db.products.updateMany({}, { $inc: { "stock": 10 } })

💡 Hint

Consider the difference between updateOne and updateMany.

updateMany updates all matching documents in one operation, which is more efficient than looping with updateOne. Option C updates all documents, not just books.