This is a Ruby on Rails 8 demo app for create, read, update, and delete actions with database optimisations using the Ruby bullet gem. It allows you to create posts with associated comments, view, edit, and delete them.
The database queries contain both unoptimised and optimised versions to see the effect of the bullet gem to indentify database performance issues and suggest improvements, such as by using eager loading of records and using the counter cache.
- Bullet gem: https://github.com/flyerhzm/bullet
The app is styled using Tailwind CSS.
- Tailwind CSS Rails gem: https://github.com/rails/tailwindcss-rails
- Tailwind CSS docs: https://tailwindcss.com/docs/
It contains model unit tests as well as integration request specs for CRUD operations - see section on tests below for more.
Install the Ruby version in the .ruby-version file then run the setup script to install the libraries and create the database.
./bin/setupYou can seed the database with some predefined posts and comments records using the command:
./bin/rails db:seedUsing the terminal navigate to the root of the project directory and run the command:
bin/devThen open your internet browser, such as Chrome, and visit http://localhost:3000/
You can create, view, edit and delete posts records as well as their associated comments.
Click on the links to view the effect of the optimised database query compared to the N+1 query warning and counter cache warning.
The test libraries used include the following Ruby gems:
The tests are located in /spec:
- Unit tests for the models are located in /spec/models
- Request tests for rendering pages and CRUD operations are located in /spec/requests
To run the test use the terminal command bin/rspec.
$ bin/rspec
Comment
associations
is expected to belong to post required: true counter_cache => true
validations
is expected to validate that :content cannot be empty/falsy
is expected to validate that the length of :content is between 3 and 255
#before_save
when :content attribute has changed and starts with a lower case letter
sets the :content attribute's fist letter to a capital letter
Post
associations
is expected to have many comments
associations
is expected to validate that :name cannot be empty/falsy
is expected to validate that the length of :name is between 3 and 255
#before_save
when :name attribute has changed and starts with a lower case letter
sets the :name attribute's fist letter to a capital letter
Posts
GET /posts
renders the table to display for posts with their comments
GET /posts/new
renders the new post page
POST /posts
creates a new post record and redirects to post show page
GET /posts/:id
renders the post show page with associated comments
GET /posts/:id/edit
renders the post edit page with associated comments
PATCH /posts/:id/edit
updates the post and redirects to post show page
DELETE /posts/:id
deletes the post and redirects to posts index page
Finished in 0.09225 seconds (files took 0.88722 seconds to load)
15 examples, 0 failures
The example database queries used for the bullet gem demo in this app are located in the PostsController.
The optimised query is to eager load the post record's associated comments in the #index controller action.
# app/controllers/posts_controller.rb
# Eager load comments to avoid N+1 queries
@posts = Post.includes(:comments)When there is an N+1 query detected the Bullet gem should trigger errors to be displayed with suggestions for improving the query performance, like the following message:
USE eager loading detected
Post => [:comments]
Add to your query: .includes([:comments])
An example in this demo app is when it loads all post records in the posts controller then loads the associated comments records in the index view file via the posts table partial.
# app/controllers/posts_controller.rb
@posts = Post.all# app/views/posts/_table.html.erb
<% post.comments.each do |comment| %>When records are loaded and then counted using the #count method without using a counter cache the Bullet gem triggers a warning.
This can be seen in the demo app when post records load their associated comments then count them using post.comments.count rather than using the counter cache that is accessed using post.comments_count.
The Comment model has counter_cache set to true for its belongs_to association with the Post model.
# app/models/comment.rb
class Comment < ApplicationRecord
belongs_to :post, counter_cache: trueThe counter cache warning can be set to true in the controller and then triggered in the posts table partial.
# app/views/posts/_table.html.erb
<% comments_count = @counter_cache_warning ? post.comments.count : post.comments_count %>
<%= pluralize(comments_count, 'Comment') %>:The query can also be manually run in the rails console using bin/rails c and running the following code to see the additional query for the count that is activated.
rails-database-performance-bullet-gem-demo(dev)> Post.first.comments_count
Post Load (0.5ms) SELECT "posts".* FROM "posts" ORDER BY "posts"."id" ASC LIMIT 1 /*application='RailsDatabasePerformanceBulletGemDemo'*/
=> 2
rails-database-performance-bullet-gem-demo(dev)> Post.first.comments.count
Post Load (0.5ms) SELECT "posts".* FROM "posts" ORDER BY "posts"."id" ASC LIMIT 1 /*application='RailsDatabasePerformanceBulletGemDemo'*/
Comment Count (0.2ms) SELECT COUNT(*) FROM "comments" WHERE "comments"."post_id" = 1 /*application='RailsDatabasePerformanceBulletGemDemo'*/
=> 2
This app's webpages are styled using Tailwind CSS.
The customised CSS styles for the app are defined in: /app/assets/tailwind/application.css
