Associations (hasMany, belongsTo) in Express - Mini Project: Build & Apply

Associations (hasMany, belongsTo) in Express with Sequelize

📖 Scenario: You are building a simple blog backend using Express and Sequelize. You want to model the relationship between Authors and their Posts. Each author can write many posts, and each post belongs to one author.

🎯 Goal: Create Sequelize models for Author and Post with the correct hasMany and belongsTo associations.

📋 What You'll Learn

Create a Sequelize model called Author with a name field of type STRING.

Create a Sequelize model called Post with a title field of type STRING.

Define a hasMany association from Author to Post.

Define a belongsTo association from Post to Author.

💡 Why This Matters

🌍 Real World

Modeling relationships between entities like authors and posts is common in blog platforms and content management systems.

💼 Career

Understanding how to define and use associations in Sequelize is essential for backend developers working with Node.js and relational databases.

1

Create Sequelize models for Author and Post

Create a Sequelize model called Author with a name field of type Sequelize.STRING. Also create a Sequelize model called Post with a title field of type Sequelize.STRING. Use sequelize.define for both models.

Express

const { Sequelize, DataTypes } = require('sequelize');
const sequelize = new Sequelize('sqlite::memory:');

// Define Author model
// Your code here

Need a hint?

Use sequelize.define('ModelName', { fieldName: DataTypes.TYPE }) to create models.

2

Create association variable for hasMany

Create a variable called authorHasManyPosts and assign it the association where Author hasMany Post.

Express

const { Sequelize, DataTypes } = require('sequelize');
const sequelize = new Sequelize('sqlite::memory:');

const Author = sequelize.define('Author', {
  name: DataTypes.STRING
});

const Post = sequelize.define('Post', {
  title: DataTypes.STRING
});

// Create hasMany association variable
// Your code here

Need a hint?

Use Author.hasMany(Post) and assign it to authorHasManyPosts.

3

Create association variable for belongsTo

Create a variable called postBelongsToAuthor and assign it the association where Post belongsTo Author.

Express

const { Sequelize, DataTypes } = require('sequelize');
const sequelize = new Sequelize('sqlite::memory:');

const Author = sequelize.define('Author', {
  name: DataTypes.STRING
});

const Post = sequelize.define('Post', {
  title: DataTypes.STRING
});

const authorHasManyPosts = Author.hasMany(Post);

// Create belongsTo association variable
// Your code here

Need a hint?

Use Post.belongsTo(Author) and assign it to postBelongsToAuthor.

4

Synchronize models with the database

Add a line to synchronize the Sequelize models with the database by calling sequelize.sync().

Express

const { Sequelize, DataTypes } = require('sequelize');
const sequelize = new Sequelize('sqlite::memory:');

const Author = sequelize.define('Author', {
  name: DataTypes.STRING
});

const Post = sequelize.define('Post', {
  title: DataTypes.STRING
});

const authorHasManyPosts = Author.hasMany(Post);
const postBelongsToAuthor = Post.belongsTo(Author);

// Synchronize models with the database
// Your code here

Need a hint?

Call sequelize.sync() to create tables based on the models and associations.