Deleting documents in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the common HTTP method used to delete a document in Express?

The DELETE method is used to remove a document or resource from the server.

beginner

How do you define a route in Express to handle deleting a document by ID?

Use app.delete('/resource/:id', (req, res) => { ... }) where ':id' is the document identifier.

beginner

What is the role of req.params in a DELETE route?

req.params contains route parameters like the document ID, which you use to identify which document to delete.

beginner

Why should you send a response after deleting a document in Express?

To inform the client that the deletion was successful or if there was an error, ensuring good communication.

beginner

What is a simple example of deleting a document from an array in Express?

Find the document by ID in the array, remove it using array methods like filter or splice, then send a response.

Which Express method is used to handle HTTP DELETE requests?

A app.post()

B app.get()

C app.delete()

D app.put()

app.delete() is the Express method designed to handle DELETE HTTP requests.

In Express, how do you access the ID parameter from the URL '/items/:id'?

A req.body.id

B req.headers.id

C req.query.id

D req.params.id

req.params.id contains the value of ':id' from the URL path.

What should you do after deleting a document in an Express route?

A Send a response to the client

B Do nothing

C Reload the server

D Close the connection without response

Always send a response to inform the client about the result of the deletion.

Which array method can be used to remove an item by ID in JavaScript?

A filter()

B map()

C reduce()

D slice()

filter() creates a new array excluding the item with the matching ID.

What status code is commonly sent after a successful DELETE request?

A 404 Not Found

B 200 OK

C 500 Internal Server Error

D 301 Moved Permanently

200 OK indicates the deletion was successful.

Explain how to set up an Express route to delete a document by its ID.

Think about the HTTP method, route parameters, and response.

Describe why sending a response after deleting a document is important in Express.

Consider communication between server and client.

Practice

1. What does the deleteOne() method do in Express when working with a database?

easy

A. Deletes a single document that matches the filter criteria.

B. Deletes all documents in the collection.

C. Updates a document instead of deleting it.

D. Finds a document but does not delete it.

Solution

1. Step 1: Understand deleteOne() purpose

   The deleteOne() method removes only one document that matches the given filter.

2. Step 2: Compare with other methods

   deleteMany() deletes multiple documents, and find() only retrieves data without deleting.

3. Final Answer:

   Deletes a single document that matches the filter criteria. -> Option A

4. Quick Check:

   deleteOne() = deletes one document [OK]

Hint: Remember: deleteOne removes just one matching document [OK]

Common Mistakes:

• Confusing deleteOne with deleteMany
• Thinking deleteOne updates documents
• Assuming deleteOne finds but does not delete

2. Which of the following is the correct syntax to delete a document by its ID using Mongoose in Express?

easy

A. Model.findByIdAndDelete(id, callback);

B. Model.deleteById(id);

C. Model.removeById(id);

D. Model.deleteOneById(id);

Solution

1. Step 1: Recall Mongoose method for deleting by ID

   The correct method is findByIdAndDelete() which deletes a document by its ID.

2. Step 2: Check syntax correctness

   Only Model.findByIdAndDelete(id, callback); matches the official Mongoose syntax.

3. Final Answer:

   Model.findByIdAndDelete(id, callback); -> Option A

4. Quick Check:

   Use findByIdAndDelete to delete by ID [OK]

Hint: Use findByIdAndDelete to remove by ID [OK]

Common Mistakes:

• Using non-existent methods like deleteById
• Confusing deleteOne with findByIdAndDelete
• Missing callback or async handling

3. What will be the output of this code snippet in Express using Mongoose?

Model.deleteMany({ status: 'inactive' })
  .then(result => console.log(result.deletedCount))
  .catch(err => console.error(err));

medium

A. An error because deleteMany does not return deletedCount.

B. The entire deleted documents array.

C. Number of documents deleted with status 'inactive'.

D. Undefined because deleteMany returns nothing.

Solution

1. Step 1: Understand deleteMany return value

   deleteMany() returns an object with deletedCount indicating how many documents were deleted.

2. Step 2: Analyze the console.log statement

   The code logs result.deletedCount, so it outputs the number of deleted documents matching the filter.

3. Final Answer:

   Number of documents deleted with status 'inactive'. -> Option C

4. Quick Check:

   deleteMany() returns deletedCount [OK]

Hint: deleteMany returns deletedCount in result object [OK]

Common Mistakes:

• Expecting deleted documents array
• Assuming deleteMany returns nothing
• Confusing deletedCount with total documents

4. Identify the error in this Express Mongoose code snippet for deleting a document:

Model.deleteOne({ _id: id }, (err, doc) => {
  if (err) console.log(err);
  else console.log(doc);
});

medium

A. The filter object is missing required fields.

B. The deleteOne method does not accept a callback.

C. The method should be deleteMany to delete one document.

D. The callback parameter doc should be result to access deletion info.

Solution

1. Step 1: Check callback parameters for deleteOne

   The second callback parameter is a result object, not the deleted document itself.

2. Step 2: Understand what doc represents

   It should be named result or similar to reflect it contains deletion info like deletedCount, not the document.

3. Final Answer:

   The callback parameter doc should be result to access deletion info. -> Option D

4. Quick Check:

   Callback gets result info, not deleted doc [OK]

Hint: Callback second param is result info, not deleted doc [OK]

Common Mistakes:

• Expecting deleted document in callback
• Using deleteMany when only one document needed
• Assuming deleteOne does not accept callbacks

5. You want to delete all documents where the field active is false, but only if the user confirms. Which Express code snippet correctly handles this with error checking?

hard

A. Model.deleteMany({ active: false }, (err, res) => {
if (err) throw err;
console.log(res);
});

B. if(confirm) {
Model.deleteMany({ active: false })
.then(res => console.log(`${res.deletedCount} deleted`))
.catch(err => console.error(err));
}

C. if(confirm) {
Model.deleteOne({ active: false })
.then(res => console.log(res))
.catch(err => console.error(err));
}

D. Model.deleteMany({ active: false })
.then(res => console.log(res.deletedCount))
.catch(err => console.error(err));

Solution

1. Step 1: Check user confirmation before deleting

   if(confirm) { Model.deleteMany({ active: false }) .then(res => console.log(`${res.deletedCount} deleted`)) .catch(err => console.error(err)); } uses an if(confirm) check to ensure deletion only happens after user confirmation.

2. Step 2: Verify deletion and error handling

   It uses deleteMany to delete all matching documents, logs the count, and catches errors properly.

3. Final Answer:

   if(confirm) { Model.deleteMany({ active: false }) .then(res => console.log(`${res.deletedCount} deleted`)) .catch(err => console.error(err)); } -> Option B

4. Quick Check:

   Confirm before delete, handle errors [OK]

Hint: Check confirm before deleteMany, handle errors in promise [OK]

Common Mistakes:

• Using deleteOne instead of deleteMany for multiple docs
• Not checking user confirmation before deleting
• Throwing errors instead of catching them