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app.get('/users', (req, res) => {
// handle GET request to /users
});
Here, app is an instance of the express module, and get() is a method that defines a route that matches GET requests. When a GET request is received at the /users URL, the callback function passed as the second argument will be executed.
Within the callback function, we can use the req and res objects to handle the request and send a response. For example, we might query a database for a list of users and send the results as a JSON response:
app.get('/users', async (req, res) => {
const users = await User.findAll();
res.json(users);
});
This code uses the Sequelize ORM to query a database for a list of users, and sends the results as a JSON response using the json() method of the res object.
Similar to get(), we can define routes for other HTTP methods such as post(), put(), delete(), etc. to handle other types of requests.
npm install mysql2 sequelize
Create a Sequelize instance with the database configuration:
const { Sequelize } = require('sequelize');
const sequelize = new Sequelize('database_name', 'username', 'password', {
host: 'localhost',
dialect: 'mysql'
});
Define a model for the database table:
const { Model, DataTypes } = require('sequelize');
class User extends Model {}
User.init({
firstName: {
type: DataTypes.STRING,
allowNull: false
},
lastName: {
type: DataTypes.STRING,
allowNull: false
}
}, {
sequelize,
modelName: 'user'
});
Sync the model with the database and execute queries:
sequelize.sync()
.then(() => {
return User.create({
firstName: 'John',
lastName: 'Doe'
});
})
.then(user => {
console.log(user.toJSON());
});
In this example, we create a Sequelize instance with the database configuration, define a model for the “user” table with two columns, sync the model with the database, create a new user record, and log the JSON representation of the user record to the console.
This is just a basic example, but it should give you an idea of how to set up and use a database with Node.js and Express.js. The specifics may vary depending on the database management system and ORM or ODM library you are using.
const express = require('express');
const { body, validationResult } = require('express-validator');
const app = express();
// Data validation middleware
app.post('/user', [
body('username').isLength({ min: 5 }),
body('email').isEmail(),
body('password').isLength({ min: 8 })
], (req, res) => {
const errors = validationResult(req);
if (!errors.isEmpty()) {
return res.status(400).json({ errors: errors.array() });
}
// If all validation checks pass, proceed with creating the user
// ...
});
// Error handling middleware
app.use((err, req, res, next) => {
console.error(err.stack);
res.status(500).send('Something broke!');
});
// Start the server
app.listen(3000, () => {
console.log('Server started on port 3000');
});
In this example, the body middleware from the express-validator module is used to validate the username, email, and password fields of a POST request to the /user endpoint. If any validation checks fail, an error response with a status code of 400 is sent to the client. If no validation errors occur, the request is allowed to proceed.
The error-handling middleware function is defined using the app.use() method. This function catches any errors that occur during the request and sends an appropriate error response to the client. In this example, the function simply logs the error to the console and sends a generic error message to the client with a status code of 500.
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