updateOne method in MongoDB - Mini Project: Build & Apply

Using the updateOne Method in MongoDB

📖 Scenario: You are managing a small library database. Each book has a title, author, and a status indicating if it is available or checked out.

🎯 Goal: Learn how to update a single document in a MongoDB collection using the updateOne method.

📋 What You'll Learn

Create a collection named books with three book documents.

Define a filter to find a book by its title.

Use the updateOne method to change the status of the book.

Confirm the update by including the update operation in the code.

💡 Why This Matters

🌍 Real World

Updating records in a database is common in real-world apps like libraries, stores, or user management systems.

💼 Career

Knowing how to update documents in MongoDB is essential for backend developers and database administrators.

1

Create the books collection with initial documents

Create a variable called books that represents a MongoDB collection. Insert these three documents exactly: { title: 'The Hobbit', author: 'J.R.R. Tolkien', status: 'available' }, { title: '1984', author: 'George Orwell', status: 'available' }, and { title: 'To Kill a Mockingbird', author: 'Harper Lee', status: 'checked out' }.

MongoDB

// Create the books collection and insert the three documents
// Your code here

Hint

Use db.collection('books') to get the collection and insertMany to add documents.

2

Define a filter to find the book titled '1984'

Create a variable called filter and set it to an object that finds the book with the title exactly equal to '1984'.

MongoDB

const books = db.collection('books');

await books.insertMany([
  { title: 'The Hobbit', author: 'J.R.R. Tolkien', status: 'available' },
  { title: '1984', author: 'George Orwell', status: 'available' },
  { title: 'To Kill a Mockingbird', author: 'Harper Lee', status: 'checked out' }
]);

// Create a filter to find the book with title '1984'
// Your code here

Hint

The filter is an object with the key title and value '1984'.

3

Use updateOne to change the status of '1984' to 'checked out'

Use the updateOne method on books with the filter variable and an update object that sets the status field to 'checked out'. Store the result in a variable called result.

MongoDB

const books = db.collection('books');

await books.insertMany([
  { title: 'The Hobbit', author: 'J.R.R. Tolkien', status: 'available' },
  { title: '1984', author: 'George Orwell', status: 'available' },
  { title: 'To Kill a Mockingbird', author: 'Harper Lee', status: 'checked out' }
]);

const filter = { title: '1984' };

// Use updateOne to set status to 'checked out' for the book matching filter
// Your code here

Hint

Use $set inside the update object to change the status field.

4

Complete the update operation by checking the modified count

Add a line that creates a variable called updatedCount and sets it to result.modifiedCount to know how many documents were updated.

MongoDB

const books = db.collection('books');

await books.insertMany([
  { title: 'The Hobbit', author: 'J.R.R. Tolkien', status: 'available' },
  { title: '1984', author: 'George Orwell', status: 'available' },
  { title: 'To Kill a Mockingbird', author: 'Harper Lee', status: 'checked out' }
]);

const filter = { title: '1984' };

const result = await books.updateOne(filter, { $set: { status: 'checked out' } });

// Store the number of updated documents in updatedCount
// Your code here

Hint

The modifiedCount property tells how many documents were changed.

Practice

1. What does the updateOne method do in MongoDB?

easy

A. Inserts a new document without checking existing ones.

B. Deletes all documents matching the filter.

C. Returns all documents without any update.

D. Updates a single document that matches the filter criteria.

Solution

1. Step 1: Understand the purpose of updateOne

   The updateOne method is designed to update only one document that matches the given filter.

2. Step 2: Compare with other operations

   Deleting or inserting documents are different operations; updateOne specifically updates one matching document.

3. Final Answer:

   Updates a single document that matches the filter criteria. -> Option D

4. Quick Check:

   updateOne updates one document [OK]

Hint: Remember: updateOne changes only one matching document [OK]

Common Mistakes:

• Thinking updateOne deletes documents
• Confusing updateOne with insert operations
• Assuming updateOne updates multiple documents

2. Which of the following is the correct syntax to update the field age to 30 using updateOne?

easy

A. db.collection.updateOne({name: 'John'}, {$change: {age: 30}});

B. db.collection.updateOne({name: 'John'}, {$set: {age: 30}});

C. db.collection.updateOne({name: 'John'}, {$update: {age: 30}});

D. db.collection.updateOne({name: 'John'}, {age: 30});

Solution

1. Step 1: Identify the update operator

   MongoDB requires using $set to update fields safely without replacing the whole document.

2. Step 2: Check syntax correctness

   db.collection.updateOne({name: 'John'}, {$set: {age: 30}}); uses $set correctly; other options use invalid operators or omit $set.

3. Final Answer:

   db.collection.updateOne({name: 'John'}, {$set: {age: 30}}); -> Option B

4. Quick Check:

   Use $set to update fields [OK]

Hint: Always use $set inside updateOne to change fields [OK]

Common Mistakes:

• Omitting $set and passing fields directly
• Using wrong update operators like $update or $change
• Forgetting to wrap update fields in an object

3. Given the collection documents:
{ _id: 1, name: 'Alice', age: 25 }
{ _id: 2, name: 'Bob', age: 28 }
What will be the result of this operation?
db.collection.updateOne({name: 'Alice'}, {$set: {age: 26}});
Then querying db.collection.find({name: 'Alice'})?

medium

A. [{ _id: 1, name: 'Alice', age: 26 }]

B. [{ _id: 1, name: 'Alice', age: 25 }]

C. No documents found

D. [{ _id: 2, name: 'Bob', age: 28 }]

Solution

1. Step 1: Understand updateOne effect

   The updateOne matches the document with name: 'Alice' and updates the age to 26.

2. Step 2: Query after update

   Querying for name: 'Alice' returns the updated document with age: 26.

3. Final Answer:

   [{ _id: 1, name: 'Alice', age: 26 }] -> Option A

4. Quick Check:

   updateOne changes age to 26 [OK]

Hint: updateOne changes one matching document's fields [OK]

Common Mistakes:

• Expecting no change after updateOne
• Confusing which document is updated
• Assuming updateOne updates multiple documents

4. What is wrong with this updateOne command?
db.collection.updateOne({name: 'Eve'}, {age: 35});

medium

A. The collection name is invalid.

B. Filter syntax is incorrect.

C. Missing $set operator to update the field.

D. The updateOne method cannot update numeric fields.

Solution

1. Step 1: Check update document structure

   The update document must use an update operator like $set to modify fields.

2. Step 2: Identify missing operator

   The command directly passes {age: 35} without $set, which replaces the entire document instead of just updating the age field.

3. Final Answer:

   Missing $set operator to update the field. -> Option C

4. Quick Check:

   Always use $set in updateOne updates [OK]

Hint: Always include $set when updating fields [OK]

Common Mistakes:

• Forgetting $set operator
• Assuming updateOne accepts direct field objects
• Misunderstanding filter vs update parts

5. You want to update the document with username: 'mike' to set active: true. If no such document exists, you want to create it with username: 'mike' and active: true. Which updateOne command achieves this?

hard

A. db.collection.updateOne({username: 'mike'}, {$set: {active: true}}, {upsert: true});

B. db.collection.updateOne({username: 'mike'}, {$set: {active: true}});

C. db.collection.updateOne({username: 'mike'}, {active: true}, {upsert: true});

D. db.collection.updateOne({username: 'mike'}, {$set: {active: true}}, {insertIfNotFound: true});

Solution

1. Step 1: Use upsert option for insert if no match

   The upsert: true option tells MongoDB to insert if no document matches the filter.

2. Step 2: Use $set to update or create fields

   The update uses $set to set active: true. The filter ensures username: 'mike' is matched or inserted.

3. Final Answer:

   db.collection.updateOne({username: 'mike'}, {$set: {active: true}}, {upsert: true}); -> Option A

4. Quick Check:

   upsert true + $set updates or inserts [OK]

Hint: Use upsert: true with $set to update or insert [OK]

Common Mistakes:

• Omitting upsert option
• Passing update fields without $set
• Using wrong option name like insertIfNotFound