Deleting documents in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when this Express route deletes a document?

Consider this Express route that deletes a user by ID from a MongoDB collection using Mongoose. What will the client receive if the user is successfully deleted?

Express

app.delete('/users/:id', async (req, res) => {
  try {
    const result = await User.findByIdAndDelete(req.params.id);
    if (!result) {
      return res.status(404).send('User not found');
    }
    res.send('User deleted');
  } catch (error) {
    res.status(500).send('Server error');
  }
});

A The client receives a JSON object with the deleted user data.

B The client always receives 'User deleted' regardless of user existence.

C The client receives a 404 error even if the user was deleted.

D The client receives 'User deleted' if the user existed and was deleted.

💡 Hint

Look at the condition checking if result is null or not.

The code checks if result is null, which means no user was found. Only if a user was found and deleted does it send 'User deleted'.

📝 Syntax

intermediate

Which option correctly deletes a document by ID in Express with Mongoose?

Choose the correct syntax to delete a document by ID using Mongoose in an Express route.

Express

app.delete('/items/:id', async (req, res) => {
  // delete code here
});

A await Item.findByIdAndRemove(req.params.id); res.send('Deleted');

B await Item.deleteById(req.params.id); res.send('Deleted');

C await Item.deleteOne({_id: req.params.id}); res.send('Deleted');

D await Item.remove({_id: req.params.id}); res.send('Deleted');

💡 Hint

Check the official Mongoose method names for deleting by ID.

findByIdAndRemove is the correct Mongoose method to delete a document by its ID. deleteById does not exist. deleteOne works but requires a filter object. remove is deprecated.

🔧 Debug

advanced

Why does this delete route always return 'User deleted' even if no user exists?

Look at this Express route code. It always sends 'User deleted' even if the user ID does not exist in the database. What is the bug?

Express

app.delete('/users/:id', async (req, res) => {
  try {
    await User.findByIdAndDelete(req.params.id);
    res.send('User deleted');
  } catch (error) {
    res.status(500).send('Server error');
  }
});

A The route should use findOneAndDelete instead of findByIdAndDelete.

B The catch block should send 'User deleted' instead of 'Server error'.

C The code does not check if the user was found before sending the response.

D The route is missing async keyword before the callback.

💡 Hint

Think about what findByIdAndDelete returns when no document is found.

findByIdAndDelete returns null if no document matches. The code does not check this and always sends 'User deleted'.

❓ state_output

advanced

What is the value of deletedCount after this delete operation?

Given this Mongoose delete operation, what will deletedCount be if the document with the given ID exists?

Express

const result = await User.deleteOne({_id: req.params.id});
const deletedCount = result.deletedCount;

A null

B 1

C undefined

D 0

💡 Hint

Check the Mongoose deleteOne result object properties.

If a document is deleted, deletedCount is 1. If none deleted, it is 0.

🧠 Conceptual

expert

Which Express middleware pattern best handles errors during document deletion?

When deleting documents in Express routes, which pattern is best to catch and handle errors globally?

A Use try-catch inside each route and call <code>next(error)</code> on catch to pass errors to error middleware.

B Use only <code>res.status(500).send()</code> inside catch blocks without calling <code>next()</code>.

C Wrap all routes in <code>Promise.resolve()</code> to catch errors automatically.

D Ignore errors and rely on Express default error handler.

💡 Hint

Think about how Express error middleware works with next().

Calling next(error) inside catch blocks passes errors to centralized error middleware, which is best practice for maintainability.