Eager loading (N+1 prevention) in Ruby on Rails - Mini Project: Build & Apply

Eager loading (N+1 prevention) in Rails

📖 Scenario: You are building a simple blog application where each Post has many Comments. You want to display a list of posts along with their comments efficiently.

🎯 Goal: Learn how to use Rails includes method to eager load associated comments for posts, preventing the N+1 query problem.

📋 What You'll Learn

Create a Post model with a has_many :comments association

Create a Comment model with a belongs_to :post association

Write a query to fetch all posts

Add eager loading of comments using includes to prevent N+1 queries

Display posts with their comments in a view

💡 Why This Matters

🌍 Real World

Eager loading is used in web applications to efficiently load related data and avoid slow database queries that happen when loading associations one by one.

💼 Career

Understanding and preventing N+1 queries is a key skill for Rails developers to build fast and scalable applications.

1

Set up Post and Comment models with associations

Create a Post model with has_many :comments and a Comment model with belongs_to :post associations.

Ruby on Rails

# Add Post and Comment models with associations here

Need a hint?

Use has_many in Post and belongs_to in Comment to set up associations.

2

Fetch all posts without eager loading

Write a query to fetch all posts and assign it to a variable called posts using Post.all.

Ruby on Rails

class Post < ApplicationRecord
  has_many :comments
end

class Comment < ApplicationRecord
  belongs_to :post
end

# Fetch all posts
# Your code here

Need a hint?

Use Post.all to get all posts and assign to posts.

3

Add eager loading of comments to prevent N+1 queries

Modify the query to fetch all posts with their comments eagerly loaded using includes(:comments) and assign it to posts.

Ruby on Rails

class Post < ApplicationRecord
  has_many :comments
end

class Comment < ApplicationRecord
  belongs_to :post
end

# Fetch all posts with comments eager loaded
# Your code here

Need a hint?

Use Post.includes(:comments).all to eager load comments with posts.

4

Display posts with their comments in a view

In a Rails view, use a each loop to iterate over posts and display each post's title and its comments' content.

Ruby on Rails

  
  # Your code here

Need a hint?

Use nested each loops to show posts and their comments.