Updating documents in Express - Performance & Optimization

Performance: Updating documents

MEDIUM IMPACT

This affects server response time and client perceived latency when updating data that triggers UI changes.

Updating a document in a database and sending the updated data to the client

Express

app.put('/item/:id', async (req, res) => {
  const id = req.params.id;
  const update = req.body;
  const result = await db.collection('items').findOneAndUpdate(
    {_id: new ObjectId(id)},
    {$set: update},
    {returnDocument: 'after'}
  );
  res.send(result.value);
});

Single atomic database call reduces latency and server load.

📈 Performance GainSaves 50-100ms per request by avoiding redundant DB fetch

Updating a document in a database and sending the updated data to the client

Express

app.put('/item/:id', async (req, res) => {
  const id = req.params.id;
  const update = req.body;
  const doc = await db.collection('items').findOne({_id: new ObjectId(id)});
  Object.assign(doc, update);
  await db.collection('items').updateOne({_id: new ObjectId(id)}, {$set: doc});
  res.send(doc);
});

Fetching the document first then updating causes two database operations and delays response.

📉 Performance CostBlocks response for extra 50-100ms due to double DB calls

Performance Comparison

Pattern	DB Calls	Server Delay	Network Payload	Verdict
Fetch then update	2 calls (findOne + updateOne)	High (extra 50-100ms)	Larger (full doc sent back)	[X] Bad
Atomic findOneAndUpdate	1 call	Low (minimal delay)	Smaller (only updated doc)	[OK] Good

Rendering Pipeline

Updating documents on the server affects the time until the client receives updated data and can re-render UI. The server processing delays INP (input responsiveness) as the client waits for confirmation.

→Server Processing

→Network Transfer

→Client Rendering

⚠️ BottleneckServer Processing due to multiple DB calls or inefficient updates

Core Web Vital Affected

INP

This affects server response time and client perceived latency when updating data that triggers UI changes.

Optimization Tips

1Use atomic update operations to reduce database calls.

2Send minimal updated data to the client to reduce network payload.

3Batch updates when possible to avoid multiple server round-trips.

Performance Quiz - 3 Questions

Which update pattern reduces server processing time when updating a document?

A Sending the entire document back to the client after update

B Using a single atomic update operation like findOneAndUpdate

C Fetching the document first, then updating it separately

D Updating the document multiple times in a loop

DevTools: Network

How to check: Open DevTools Network tab, perform the update request, and observe the request duration and response size.

What to look for: Look for longer request times and larger response payloads indicating inefficient updates.

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