Deleting documents in Express - Mini Project: Build & Apply

Deleting Documents with Express

📖 Scenario: You are building a simple web server using Express. This server manages a list of documents stored in memory. You want to add the ability to delete a document by its ID.

🎯 Goal: Build an Express server that stores documents in an array and allows deleting a document by its id using a DELETE request.

📋 What You'll Learn

Create an array called documents with three objects, each having id and title properties.

Create a variable called deleteId and set it to 2.

Use the filter method on documents to remove the document with id equal to deleteId.

Add an Express DELETE route at /documents/:id that deletes the document with the given id from documents.

💡 Why This Matters

🌍 Real World

Deleting documents or records is a common feature in web applications like content management systems, note-taking apps, or admin dashboards.

💼 Career

Understanding how to handle DELETE requests and manipulate data collections is essential for backend developers working with REST APIs.

1

Create the initial documents array

Create an array called documents with these exact objects: { id: 1, title: 'Doc One' }, { id: 2, title: 'Doc Two' }, and { id: 3, title: 'Doc Three' }.

Express

// Create the documents array with 3 objects
// Your code here

Hint

Use const documents = [ ... ] with three objects inside.

2

Set the ID to delete

Create a variable called deleteId and set it to the number 2.

Express

const documents = [
  { id: 1, title: 'Doc One' },
  { id: 2, title: 'Doc Two' },
  { id: 3, title: 'Doc Three' }
];

// Create deleteId variable
// Your code here

Hint

Use const deleteId = 2; to store the ID to delete.

3

Filter out the document to delete

Use the filter method on documents to create a new array without the document whose id equals deleteId. Assign this new array back to documents.

Express

const documents = [
  { id: 1, title: 'Doc One' },
  { id: 2, title: 'Doc Two' },
  { id: 3, title: 'Doc Three' }
];

const deleteId = 2;

// Filter documents to remove the one with id equal to deleteId
// Your code here

Hint

Use documents = documents.filter(doc => doc.id !== deleteId); to remove the document.

4

Add Express DELETE route to delete documents

Add an Express DELETE route at /documents/:id. Inside the route, convert req.params.id to a number, then update documents by filtering out the document with that id. Send a JSON response with { message: 'Document deleted' }.

Express

let documents = [
  { id: 1, title: 'Doc One' },
  { id: 2, title: 'Doc Two' },
  { id: 3, title: 'Doc Three' }
];

const deleteId = 2;

documents = documents.filter(doc => doc.id !== deleteId);

const express = require('express');
const app = express();

// Add DELETE route at /documents/:id
// Your code here

Hint

Use app.delete('/documents/:id', (req, res) => { ... }) and inside convert req.params.id to a number, then filter documents, then send JSON response.

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