Q1. How do you implement CREATE operation in Express with database?
For POST route, extract data from req.body, validate, then insert into database. With Mongoose: const user = new User(req.body); await user.save(); res.status(201).json(user). With SQL: await db.query('INSERT INTO users SET ?', [req.body]).
Q2. How do you implement READ operation?
GET routes to fetch data. For all items: await User.find() or SELECT * FROM users. For single item with ID: await User.findById(req.params.id) or SELECT * FROM users WHERE id = ?. Handle 404 if not found.
Q3. How do you implement UPDATE operation?
PUT or PATCH routes. Get ID from params, updated data from body. With Mongoose: await User.findByIdAndUpdate(req.params.id, req.body, { new: true }). With SQL: UPDATE users SET ? WHERE id = ?. Return updated item.
Q4. How do you implement DELETE operation?
DELETE route with ID. With Mongoose: await User.findByIdAndDelete(req.params.id). With SQL: DELETE FROM users WHERE id = ?. Usually return 204 No Content or the deleted item. Check if item existed first.
Q5. What validation should you perform in CRUD operations?
Always validate input: check required fields, data types, formats (email), lengths. Handle duplicate entries. Validate that items exist before updating/deleting. Use libraries like Joi or express-validator. Never trust client input.