Updating documents in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the common method used in Express to update a document in a database?

The common method is using HTTP PUT or PATCH requests handled by Express routes, which then call database update functions.

intermediate

In Express, what is the difference between PUT and PATCH when updating documents?

PUT replaces the entire document, while PATCH updates only specified fields.

beginner

How do you access data sent by the client to update a document in Express?

You access data from the request body using middleware like express.json() and then use req.body in your route handler.

beginner

What is a typical Express route handler signature for updating a document?

It usually looks like: app.put('/items/:id', (req, res) => { /* update logic */ }); where :id is the document identifier.

intermediate

Why is it important to validate data before updating documents in Express?

Validating data ensures only correct and safe data updates the document, preventing errors and security issues.

Which HTTP method is typically used in Express to update part of a document?

A POST

B GET

C DELETE

D PATCH

PATCH is used to update parts of a document, while GET retrieves data, POST creates, and DELETE removes.

How do you parse JSON data sent in the request body in Express?

A Using express.json() middleware

B Using express.urlencoded() middleware

C Using body-parser deprecated package only

D No middleware needed

express.json() middleware parses incoming JSON request bodies so you can access data via req.body.

In Express, where do you find the document ID when updating a document via URL?

A req.body

B req.params

C req.query

D req.headers

req.params contains route parameters like :id used in the URL path.

What should you do before updating a document with user data in Express?

A Delete the document first

B Ignore validation

C Validate the data

D Send a GET request

Validating data prevents invalid or harmful data from corrupting the document.

Which Express method handles full replacement of a document?

A PUT

B PATCH

C GET

D POST

PUT replaces the entire document, while PATCH updates parts of it.

Explain how to set up an Express route to update a document using the PATCH method.

Think about how the route, middleware, and request data work together.

Describe why validating user input is important before updating documents in Express applications.

Consider both technical and user experience reasons.

Practice

1. What does the findByIdAndUpdate method do in Express with Mongoose?

easy

A. It updates a document by its ID and returns the updated document.

B. It deletes a document by its ID.

C. It creates a new document with a given ID.

D. It finds a document but does not update it.

Solution

1. Step 1: Understand the method purpose

   findByIdAndUpdate is used to find a document by its ID and update it with new data.

2. Step 2: Check the return value

   When used with { new: true }, it returns the updated document, not the old one.

3. Final Answer:

   It updates a document by its ID and returns the updated document. -> Option A

4. Quick Check:

   Update document by ID = A [OK]

Hint: Remember: findByIdAndUpdate updates and returns new data [OK]

Common Mistakes:

• Confusing update with delete operation
• Expecting it to create a new document
• Thinking it only finds without updating

2. Which of the following is the correct syntax to update a document by ID and return the updated document in Express with Mongoose?

easy

A. Model.findOneAndUpdate(id, update);

B. Model.updateById(id, update, callback);

C. Model.update(id, update, { returnNew: true });

D. Model.findByIdAndUpdate(id, update, { new: true }, callback);

Solution

1. Step 1: Identify correct method and parameters

   The correct method is findByIdAndUpdate with parameters: id, update object, options, and callback.

2. Step 2: Confirm option for returning updated document

   The option { new: true } ensures the updated document is returned.

3. Final Answer:

   Model.findByIdAndUpdate(id, update, { new: true }, callback); -> Option D

4. Quick Check:

   Correct syntax includes { new: true } = C [OK]

Hint: Use { new: true } option to get updated document [OK]

Common Mistakes:

• Using wrong method name like updateById
• Omitting the { new: true } option
• Passing incorrect parameters order

3. Given the code snippet:

Model.findByIdAndUpdate('123', { name: 'Alice' }, { new: true }, (err, doc) => {
  if (err) return console.error(err);
  console.log(doc.name);
});

What will be printed if the update is successful?

medium

A. The old name before update

B. Alice

C. undefined

D. An error message

Solution

1. Step 1: Understand the update and options

   The update changes the name to 'Alice' and { new: true } returns the updated document.

2. Step 2: Check the console output

   The callback logs doc.name, which will be 'Alice' after update.

3. Final Answer:

   Alice -> Option B

4. Quick Check:

   Updated document name logged = B [OK]

Hint: With { new: true }, console logs updated value [OK]

Common Mistakes:

• Expecting old value instead of updated
• Not using { new: true } option
• Misreading callback parameters

4. Identify the error in this code snippet for updating a document:

Model.findByIdAndUpdate('123', { age: 30 }, (err, doc) => {
  if (err) console.log(err);
  else console.log(doc);
});

medium

A. The update object should be a string

B. Using wrong method name, should be updateById

C. Missing the { new: true } option to get updated document

D. Callback function parameters are incorrect

Solution

1. Step 1: Check method usage

   The method findByIdAndUpdate is correct and callback parameters are valid.

2. Step 2: Identify missing option

   Without { new: true }, the returned document is the old one, not updated.

3. Final Answer:

   Missing the { new: true } option to get updated document -> Option C

4. Quick Check:

   Return updated doc requires { new: true } = D [OK]

Hint: Add { new: true } to get updated document in callback [OK]

Common Mistakes:

• Assuming updateById is a valid method
• Expecting updated doc without { new: true }
• Thinking update object must be string

5. You want to update a user's email only if the new email is not empty and valid. Which approach correctly updates the document safely in Express with Mongoose?

hard

A. Check email validity before calling findByIdAndUpdate, then update with { new: true } option.

B. Call findByIdAndUpdate directly without validation to save time.

C. Use findByIdAndUpdate with an empty update object if email is invalid.

D. Update the document without callback and ignore errors.

Solution

1. Step 1: Validate input before updating

   Always check if the new email is valid and not empty before updating to avoid bad data.

2. Step 2: Use findByIdAndUpdate with { new: true }

   Update the document with the valid email and use { new: true } to get the updated document.

3. Final Answer:

   Check email validity before calling findByIdAndUpdate, then update with { new: true } option. -> Option A

4. Quick Check:

   Validate input + update with new:true = A [OK]

Hint: Always validate input before updating documents [OK]

Common Mistakes:

• Skipping validation and risking bad data
• Updating with empty or invalid data
• Ignoring errors by not using callbacks