CRUD Operations with MongoDB in Node.js Interview Questions

Q1. How do you create (insert) documents in MongoDB?

With MongoDB driver:

const result = await db.collection('users').insertOne({
  name: 'John',
  age: 30
});

For multiple: insertMany([...]). With Mongoose:

const user = new User({ name: 'John' });
await user.save();

User.create({ name: 'John' });

The inserted document includes an _id field automatically.

Q2. How do you read (query) documents?

With MongoDB driver:

const users = await db.collection('users')
  .find({ age: { $gt: 18 } })
  .toArray();

For single: findOne({ _id: ObjectId(id) }). With Mongoose:

const users = await User.find({ age: { $gt: 18 } });
const user = await User.findById(id);

Queries support filtering, projection, sorting, and pagination.

Q3. How do you update documents?

With MongoDB driver:

await db.collection('users').updateOne(
  { _id: id },
  { $set: { age: 31 } }
);

For multiple: updateMany(). With Mongoose:

await User.updateOne(
  { _id: id },
  { $set: { age: 31 } }
);

or find and update:

await User.findByIdAndUpdate(id, { age: 31 }, { new: true });

The $set operator updates specific fields.

Q4. How do you delete documents?

With MongoDB driver:

await db.collection('users').deleteOne({ _id: id });

or deleteMany(). With Mongoose:

await User.deleteOne({ _id: id });

await User.findByIdAndDelete(id);

Be careful with delete operations as they are irreversible. Consider soft deletes by adding a deleted flag instead.

Q5. How do you handle errors in CRUD operations?

Use try/catch blocks. Common errors: duplicate key (E11000), validation errors, cast errors (invalid ObjectId), connection errors. Example:

try {
  await user.save();
} catch (err) {
  if (err.code === 11000) {
    // duplicate key error
  } else {
    // handle other errors
  }
}

Always send appropriate HTTP status codes.

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