How to Use Sequelize in Node.js: Simple Guide

To use Sequelize in Node.js, first install it with a database driver, then create a Sequelize instance to connect to your database. Define models to represent tables, and use Sequelize methods to query or update data asynchronously.

Syntax

Sequelize uses a simple pattern: create a Sequelize instance with database details, define models with sequelize.define(), and perform operations like findAll() or create().

Each model represents a table, and fields define columns. Sequelize methods return promises, so use async/await to handle results.

javascript

import { Sequelize, DataTypes } from 'sequelize';

// Create connection
const sequelize = new Sequelize('database', 'username', 'password', {
  host: 'localhost',
  dialect: 'mysql' // or 'postgres', 'sqlite', etc.
});

// Define a model
const User = sequelize.define('User', {
  username: {
    type: DataTypes.STRING,
    allowNull: false
  },
  birthday: {
    type: DataTypes.DATE
  }
});

// Use model methods
async function example() {
  await sequelize.sync(); // create tables if not exist
  const user = await User.create({ username: 'jane', birthday: new Date(1990, 6, 20) });
  const users = await User.findAll();
  console.log(users);
}

Example

This example shows how to connect to a SQLite database, define a Task model, add a task, and fetch all tasks.

javascript

import { Sequelize, DataTypes } from 'sequelize';

// Connect to SQLite database in memory
const sequelize = new Sequelize('sqlite::memory:');

// Define Task model
const Task = sequelize.define('Task', {
  title: {
    type: DataTypes.STRING,
    allowNull: false
  },
  done: {
    type: DataTypes.BOOLEAN,
    defaultValue: false
  }
});

async function run() {
  await sequelize.sync(); // create tables

  // Create a new task
  await Task.create({ title: 'Learn Sequelize' });

  // Fetch all tasks
  const tasks = await Task.findAll();
  tasks.forEach(task => {
    console.log(`Task: ${task.title}, Done: ${task.done}`);
  });
}

run();

Output

Task: Learn Sequelize, Done: false

Common Pitfalls

• Not awaiting sequelize.sync() before querying can cause errors because tables may not exist yet.
• Forgetting to handle asynchronous calls with async/await or .then() leads to unexpected results.
• Using wrong dialect or missing database driver causes connection failures.
• Not defining allowNull properly can cause validation errors.

javascript

/* Wrong: Missing await on sync */
sequelize.sync();
User.create({ username: 'bob' }); // May fail if table not ready

/* Right: Await sync before queries */
await sequelize.sync();
await User.create({ username: 'bob' });

Quick Reference

Here is a quick summary of common Sequelize methods:

Method	Description
sequelize.define(name, attributes)	Define a new model (table)
sequelize.sync()	Create tables if they don't exist
Model.create(data)	Add a new record
Model.findAll()	Get all records
Model.findOne({ where })	Get one record matching condition
Model.update(data, { where })	Update records matching condition
Model.destroy({ where })	Delete records matching condition

Key Takeaways

Install Sequelize and a database driver before use.

Create a Sequelize instance with your database info.

Define models to represent tables and their columns.

Use async/await to handle Sequelize's asynchronous methods.

Always sync your models before querying the database.