How to: Benchmark an Active Record query with a Ruby script
Recently I needed to benchmark an Active Record query for performance measurements. I wrote a small script that runs each query to benchmark 100 times and calculates the 95th percentile.
Note: The script requires sudo permissions to drop RAM cache of PostgreSQL. Due to the number of iterations it was impractical to enter my user password that often. And I temporary edited my /etc/sudoers
to not ask for the sudo password with johndoe ALL=(ALL) NOPASSWD: ALL
.
# Run this script with e.g. `rails ru...
Implementing a custom RuboCop cop
It's possible to implement simple custom RuboCop cops with very little code. They work exactly the same like existing rubocop cops and fail the pipeline if they find an offense. This is handy for project specific internal rules or conventions.
The following cop looks at every ruby file and searches for TODO
or WIP
comments and adds an offense.
class NoTodos < RuboCop::Cop::Base
MSG = "Don't add TODOs & WIPs in the source."
def on_new_investigation
processed_source.comments.each { |comment| search_for_forbidden_ann...
Compare library versions as "Gem::Version" instances, not as strings
Sometimes we have to write code that behaves differently based on the version of a specific gem or the Ruby Version itself. The version comparison can often be seen with simple string comparison like so.
# ❌ Not recommended
if Rails.version > '6.1.7.8' || RUBY_VERSION > '3.1.4'
raise Error, 'please check if the monkey patch below is still needed'
end
If you are lucky, the version comparison above works by coincidence. But chances are that you are not: For example, Rails version 6.1.10.8
would not raise an error in the code ...
A gotcha of Ruby variable scoping
I recently stumbled over a quirk in the way Ruby handles local variables that I find somewhat dangerous.
Consider:
def salutation(first_name, last_name = nil)
if last_name
full_name = "#{first_name} #{last_name}"
end
"Hi #{full_name}"
end
This is obviously wrong, full_name
is unset when last_name
is nil.
However, Ruby will not raise an exception. Instead, full_name
will simply be nil
, and salutation('Bob')
returns 'Hi '
.
The same would happen in an else
branch:
def salutation(fi...
How to speed up JSON rendering with Rails
I was recently asked to optimize the response time of a notoriously slow JSON API endpoint that was backed by a Rails application.
While every existing app will have different performance bottlenecks and optimizing them is a rabbit hole of arbitrary depth, I'd like to demonstrate a few techniques which could help reaching actual improvements.
The baseline
The data flow examined in this card are based on an example barebone rails app, which can be used to reproduce the r...
How to query GraphQL APIs with Ruby
While most Rails Apps are tied to at least one external REST API, machine-to-machine communication via GraphQL is less commonly seen. In this card, I'd like to give a quick intro on how to query a given GraphQL API - without adding any additional library to your existing app.
Core aspects of GraphQL
Interacting with GraphQL feels a bit like querying a local database. You are submitting queries to fetch data in a given structure (like SELECT in SQL) or mutations to alter the database (similar to POST/PUT/DELETE in REST). You can ...
Rails npm packages will use an uncommon versioning scheme
When Rails releases a new version of their gems, they also release a number of npm packages
like @rails/activestorage
or @rails/actioncable
.
Unfortunately Rails uses up to 4 digits for their gem version, while npm only allows 3 digits and a pre-release suffix.
To map gem versions and npm versions, Rails is going to use a naming scheme like this:
Gem version | npm version |
---|---|
7.0.0 |
7.0.0 |
7.0.1 |
7.0.100 |
... |
Ruby: Retrieving and processing files via Selenium and JavaScript
This card shows an uncommon way to retrieve a file using selenium where JavaScript is used to return a binary data array to Ruby code.
The following code example retrieves a PDF but the approach also works for other file types.
require "selenium-webdriver"
selenium_driver = Selenium::WebDriver.for :chrome
selenium_driver.navigate.to('https://example.com')
link_to_pdf = 'https://blobs.example.com/random-pdf'
binary_data_array = selenium_driver.execute_script(<<-JS, link_to_pdf)
const response = await fetch(arguments[0])
if (!r...
Bundler: Enforce consistent platform versions
Some rubygems come in platform-specific versions (i.e. "x86_64-linux") in addition to the usual "ruby" platform. This is often is done for gems with native extensions that want to deliver precompiled binaries for ease of installation. However, there is an issue on some versions of Bundler (at least 2.3.x) that makes it inconsistent which versions of a gem will be installed.
Why this happens
On (very) old versions of Bundler, the Gemfile.lock
could never indicate which version of a gem was installed, i.e. the Gemfile read `nokogiri (1....
Upgrading RubyGems to the last compatible version
Running gem update --system
will install the latest version of RubyGems. However the latest version might not be compatible with your current version of Ruby.
To install the latest version that is compatible with your Ruby:
- Go to the version history and find the latest compatible version (any Ruby constraint can be found in the right sidebar)
- Append that version to the
update
command. E.g. to install the latest version compatible with Ruby 2:gem update --system 3.4.22
...
Ruby: How to make your ruby library configurable
You might know a few examples, where you configure some library via a block. One example is the Rails configuration:
Rails.application.configure do |config|
config.enable_reloading = false
end
This card describes a simple example on how to make your ruby library configurable.
Example
module FooClient
class Client
class_attribute :config
def self.configure
self.config ||= Configuration.new
yield(config)
end
def test
uri = URI.parse(FooClient::Client.config.endpoint)
Net:...
Rails: Example on how to extract domain independent code from the `app/models` folder to the `lib/` folder
This cards describes an example with a Github Client on how to keep your Rails application more maintainable by extracting domain independent code from the app/models
folder to the lib/
folder. The approach is applicable to arbitrary scenarios and not limited to API clients.
Example
Let's say we have a Rails application that synchronizes its users with the Github API:
.
└── app
└── models
├── user
│ ├── github_client.rb
│ └── sychronizer.rb
└── user.rb
In this example the app folder ...
Ruby: Different ways of assigning multiple attributes
This card is a short summary on different ways of assigning multiple attributes to an instance of a class.
Using positional parameters
Using parameters is the default when assigning attributes. It works good for a small number of attributes, but becomes more difficult to read when using multiple attributes.
Example:
class User
def initialize(salutation, first_name, last_name, street_and_number, zip_code, city, phone_number, email, newsletter)
@salutation = salutation
@first_name = first_name
@last_name = last_nam...
routing-filter is broken with Rails 7.1
If you are using the routing-filter gem in your Rails 7.1 app for managing URL segments for locales or suffixes, you will notice that the filters do no longer apply, routes are broken and the necessary parameters are no longer extracted. That is because routing-filter patches Rails' find_routes
-method to get the current path and apply its defined filters on it. These filters then modify the params that are handed over to your controller action. This way you receive a locale
parameter from a ...
makandra cards: A knowledge base on web development, RoR, and DevOps
What is makandra cards?
We are makandra, a team of 60 web developers, DevOps and UI/UX experts from Augsburg, Germany. We have firmly anchored the sharing of knowledge and continuous learning in our company culture. Our makandra cards are our internal best practices and tips for our daily work. They are read worldwide by developers looking for help and tips on web development with Ruby on Rails and DevOps.
15 years ago – in 2009 – we wrote our first card. Since then, over 6000 cards have been created, not o...
Ruby: Following redirects with the http gem ("httprb")
When making requests using the http
gem you might want to automatically follow redirects to get the desired response. This is supported but not the default behavior.
You can do so by using the .follow
method.
This follows redirects for the following status codes: 300, 301, 302, 303, 307, 308
response = HTTP.get('https://www.example.com/redirect')
response.status # => 302
response.uri.to_s # => "https://www.example.com/redirect"
response = HTTP.follow.get('https://www.example.com/redirect')
response.status # => 200
response....
Using rack-mini-profiler (with Unpoly)
Debugging performance issues in your Rails app can be a tough challenge.
To get more detailed insights consider using the rack-mini-profiler gem.
Setup with Unpoly
Add the following gems:
group :development do
gem 'memory_profiler'
gem 'rack-mini-profiler'
gem 'stackprof'
end
Unpoly will interfere with the rack-mini-profiler widget, but configuring the following works okayish:
// rack-mini-profiler + unpoly
if (process...
Ruby: How to connect to a host with expired SSL certificate
If you need to make an HTTPS connection to a host which uses an expired certificate, do not disable certificate verifications entirely. Doing that enables e.g. man in the middle attacks.
If you accept only a single expired and known certificate, you are much less in trouble.
Setup
All the solutions described below use a verify_callback
for the request's OpenSSL::X509::Store
where you can specify a lambda to adjust its verification response.
Your callback must return either true
or false
and OpenSSL's verification result is...
List of handy Ruby scripts to transcode different file types (often by using GPT)
It's 2024 and we have tools like ffmpeg, imagemagick and GPT readily available. With them, it's easy to convert texts, images, audio and video clips into each other.
For the everyday use without any parameter tweaking I'm using a collection of tiny scripts in my ~/bin
folder that can then be used as bash functions. And: It's faster to use the CLI than interacting with a website and cheaper to use the API than buying GPT plus.. :-)
Usage
text-to-image "parmiggiano cheese wedding cake, digital art"
- `text-to-audio "Yesterday I ate ...
Use <input type="number"> for numeric form fields
Any form fields where users enter numbers should be an <input type="number">
.
Numeric inputs have several benefits over <input type="text">
:
- On mobile or tablet devices, number fields show a special virtual keyboard that shows mostly digit buttons.
- Decimal values will be formatted using the user's language settings.
For example, German users will see1,23
for<input type="number" value="1.23">
. - Values in the JavaScript API or when submitting forms to the server will always use a point as decimal separator (i.e.
"1.23"
eve...
CI Template for GitHub Actions
Usually our code lives on GitLab, therefore our documentation for CI testing is extensive in this environment. If you are tied to GitHub e.g. because your customer uses it, you may use the following GitHub Actions template for the CI integration. It includes jobs for rspec
(parallelized using knapsack, unit + feature specs), rubocop
, eslint
, coverage
and license_finder
.
Note that GitHub does not allow the use of YAML anchors and aliases. You can instead use [compos...
How to configure Selenium WebDriver to not automatically close alerts or other browser dialogs
tl;dr
We recommend configuring Selenium's unhandled prompt behavior to
{ default: 'ignore' }
with the monkey patch below.
When running tests in a real browser, we use Selenium. Each browser is controlled by a specific driver, e.g. Selenium::WebDriver::Chrome
for Chrome.
There is one quirk to all drivers (at least those following the W3C webdriver spec) that can be impractical:
When any user prompt (like an alert
) is encountered when trying to perform an action, they will [...
Bash: How to count and sort requests by IP from the access logs
Example
87.140.79.42 - - [23/Jan/2024:09:00:46 +0100] "GET /monitoring/pings/ HTTP/1.1" 200 814 "-" "Ruby"
87.140.79.42 - - [23/Jan/2024:09:00:46 +0100] "GET /monitoring/pings/ HTTP/1.1" 200 814 "-" "Ruby"
87.140.79.41 - - [23/Jan/2024:09:00:46 +0100] "GET /monitoring/pings/ HTTP/1.1" 200 814 "-" "Ruby"
87.140.79.42 - - [23/Jan/2024:09:00:46 +0100] "GET /monitoring/pings/ HTTP/1.1" 200 814 "-" "Ruby"
Goal
Count and sort the number of requests for a single IP address.
Bash Command
awk '{ print $1}' test.log | sort...