Database query optimization in Ruby on Rails - Mini Project: Build & Apply

Database query optimization

📖 Scenario: You are building a simple blog application using Ruby on Rails. The app has Post and Comment models. Each post can have many comments.Currently, the app loads all posts and then loads comments for each post separately. This causes many database queries and slows down the app.

🎯 Goal: Optimize the database queries to load posts and their comments efficiently using Rails techniques.

📋 What You'll Learn

Create a Post model with a title and body

Create a Comment model with content and a post_id

Write a query to load all posts

Optimize the query to include comments to avoid N+1 queries

💡 Why This Matters

🌍 Real World

Optimizing database queries is essential for building fast and scalable web applications that handle related data efficiently.

💼 Career

Understanding query optimization in Rails is a key skill for backend developers to improve app performance and user experience.

1

Create Post and Comment models

Create a Post model with attributes title and body, and a Comment model with attributes content and post_id. Set up the association so that Post has many comments and Comment belongs to post.

Ruby on Rails

# Define Post and Comment models with associations
# Your code here

Need a hint?

Use has_many :comments in Post and belongs_to :post in Comment.

2

Load all posts

Write a query to load all posts from the database and assign it to a variable called posts.

Ruby on Rails

class Post < ApplicationRecord
  has_many :comments
end

class Comment < ApplicationRecord
  belongs_to :post
end

# Load all posts
# Your code here

Need a hint?

Use Post.all to get all posts.

3

Optimize query with includes

Modify the query to load all posts and their associated comments in one query using includes(:comments). Assign the result to the variable posts.

Ruby on Rails

class Post < ApplicationRecord
  has_many :comments
end

class Comment < ApplicationRecord
  belongs_to :post
end

# Optimize query to include comments
# Your code here

Need a hint?

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

4

Use optimized posts in view

Write a loop to iterate over posts and for each post, iterate over its comments to display the comment content. Use posts.each do |post| and post.comments.each do |comment|.

Ruby on Rails

class Post < ApplicationRecord
  has_many :comments
end

class Comment < ApplicationRecord
  belongs_to :post
end

posts = Post.includes(:comments).all

# Loop through posts and comments
# Your code here

Need a hint?

Use nested loops: posts.each do |post| and inside it post.comments.each do |comment|.