Ruby object equality
TLDR
if you define a equality method for a class you must also implement
def hash
.
Ruby has a lot of methods that have to do something with equality, like ==
, ===
, eql?
, equal?
. This card should help you differentiate between those and give you hints on how to implement your own equality methods in a safe manner.
Differences between the methods
for everyday use: ==
When you compare two objects in ruby, you most often see the use of foo == bar
. By default the ==
operator inherits from Object
and is impl...
Bookmarklet: cards Markup Link Bookmarklet
The cards editor has a feature "Cite other card" to create links to other cards in the same deck as mardown links.
If you want to reference a card from a different deck, this bookmarklet might be useful:
javascript:(function () {
const doAlert = () => { alert("Maybe not a makandra card?") };
let cardsPathPattern = /(\/[\w-]+\/\d+)-.+/;
if (window.location.pathname.match(cardsPathPattern)) {
let currentPath = window.location.pathname.match(cardsPathPattern)[1];
let title = document.querySelector('h1.note--title')?.textCon...
Rails: Use STI in Migration
tl;dr
You should decouple migrations from models by embedding models into the migration. To use STI in this scenario you have to overwrite
find_sti_class
andsti_name
.
Tip
When possible, try to avoid STI in migrations by disabling it.
Example
Warning
This is more for the sake of I want to do it but I kno...
Jasmine: Creating DOM elements efficiently
Jasmine specs for the frontend often need some DOM elements to work with. Because creating them is such a common task, we should have an efficient way to do it.
Let's say I need this HTML structure:
<ul type="square">
<li>item 1</li>
<li>item 2</li>
</ul>
This card compares various approaches to fabricating DOM elements for testing.
Constructing individual elements
While you can use standard DOM functions to individually create and append elements, this is extremely verbose:
let list = document.createElement('...
Variable fonts: Is the performance trade-off worth it? - LogRocket Blog
Variable fonts are popular for two reasons: they expand design possibilities and improve website performance. While the former statement is definitely true since variable fonts do provide infinite typographical choices, the latter only holds under certain conditions.
Chrome DevTools: Treasure (Overview)
tl;dr
The Chrome DevTools are a neat collection of tools for the daily work as a web developer. If you're lucky, you'll maybe find some handy stuff in here.
Analysing
Breakpoints
- [Breakpoints on HTML Elements](https://makandracards.com/makandra/517982-chrome-devtools...
ActiveType::Object: Be careful when overriding the initialize method
Background:
ActiveType::Object
inherits from ActiveRecod::Base
and is designed to behave like an ActiveRecord Object, just without the database persistence.
Don't remove any of the default behavior of the initialize method!
If you have a class which inherits from ActiveType::Object
and you need to override the #initialize
method, then you should be really careful:
- Always pass exactly one attribute.
ActiveRecod::Base
objects really want to get their arguments processable as keyword arguments. Don't change the syntax, or y...
Debug flaky tests with an Unpoly observeDelay
The problem
Unpoly's [up-observe]
, [up-autosubmit]
and [up-validate]
as well as their programmatic variants up.observe()
and up.autosubmit()
are a nightmare for integration tests.
Tests are usually much faster than the configured up.form.config.observeDelay
. Therefore, it may happen that you already entered something into the next field before unpoly updates that field with a server response, discarding your changes.
The steps I wait for active ajax requests to complete
(if configured) and capybara-lockstep can catch some ...
Rails: Validations of Dates, Numerics and Strings with ComparisonValidator
tl;dr
Since Rails
7+
you can useComparisonValidator
for validations likegreater_than
,less_than
, etc. on dates, numerics or strings.
Example
We have a model for booking a trip. This model has mandatory attributes to enforce dates for the start and the end.
# == Schema Information
#
# start_date :date
# end_date :date
# ...
class TripBooking < ApplicationRecord
validates :start_date, presence: true
validates :end_date, presence: true
end
These validations are enough. We also want to ensure, th...
Statistics and Reports on Web Performance Optimization
Case studies and experiments demonstrating the impact of web performance optimization (WPO) on user experience and business metrics.
Careful: `fresh_when last_modified: ...` without an object does not generate an E-Tag
To allow HTTP 304 responses, Rails offers the fresh_when
method for controllers.
The most common way is to pass an ActiveRecord instance or scope, and fresh_when
will set fitting E-Tag
and Last-Modified
headers for you. For scopes, an extra query is sent to the database.
fresh_when @users
If you do not want that magic to happen, e.g. because your scope is expens...
Rails: Custom validator for "only one of these" (XOR) presence validation
For Rails models where only one of multiple attributes may be filled out at the same time, there is no built-in validation.
I've seen different solutions in the wild, each with different downsides:
- Private method referenced via
validate
: works, but is barely portable and clutters the model. - Multiple presence validations with "if other is blank" each: looks pretty, but is incorrect as it allows both values to be filled in; also the error messages for a blank record are misleading.
Here is a third option: Write a custom validator to ...
Creating a Rails application in a single file
Greg Molnar has written a neat article about creating a single-file Rails app.
This is not meant for production use but can be useful to try things out, e.g. when hunting down a bug or embedding a Rails app into the tests of a gem.
What you do is basically:
- Put everything (gems, application config, database migrations, models, controllers) into a single
.ru
file, likeapp.ru
. - Run it via
rackup app.ru
. (Hint: if your file is calledconfig.ru
, you can just run `rac...
Git: Removing feature branches on merge
When working with feature branches, stale branches pile up over time. It's best to remove them right after merge, locally and on the remote, but it is a little tedious: you need to remember it, and perform the few steps manually each time.
Enter Git hooks. The folks at Liquid Light have built a little post-merge hook that will delete a feature branch on confirmation....
Rails: Fixing the memory leak / performance issues in prepend_view_path
Recently we detected a memory leak in one of our applications. Hunting it down, we found that the memory leak was located in Rails' #prepend_view_path
. It occurs when the instance method prepend_view_path
is called in each request, which is a common thing in a multi-tenant application.
On top of leaking memory, it also causes a performance hit, since templates rendered using the prepended view path will not be cached and compiled anew on each request.
This is not a new memory leak. It was [first reported in in 2014](https://github.com/...
A short overview of common design patterns implemented within Rails
The linked content includes a few design patterns implemented with Ruby on Rails.
What is the card indented to achieve?
- You can use the pattern names for code reviews, so all parties know with only a few words which change is requested. Example: "Please use a form object here"
- You can learn about new code patterns
- You should read the sections "Advantages of using design patterns" and "Disadvantages of using design patterns in a wrong way", since design patterns do not replace good code
Included Design Patterns: Service, Value objec...
PostgreSQL: How to show database size
SELECT pg_size_pretty(pg_database_size('some-database'));
Example
SELECT pg_size_pretty(pg_database_size('cards_p'));
----------------
13 GB
(1 row)
SELECT pg_database_size('cards_p');
pg_database_size
------------------
13524832927
(1 row)
Related
Postgresql: Paginate and count in one query using window functions
When paginating records, we usually need to know the number of total records in order to render pagination links. Popular pagination libraries like will_paginate or Kaminari do this for us by simply issuing an extra query, like this:
SELECT post.* FROM posts LIMIT 20 OFFSET 100;
SELECT COUNT(*) FROM posts;
This is fine most of the time. But rarely, you might have very complicated WHERE
conditions or a subquery that takes time to run. In thes...
Josh McArthur: Fancy Postgres indexes with ActiveRecord
I recently wanted to add a model for address information but also wanted to add a unique index to those fields that is case-insensitive.
The model looked like this:
create_table :shop_locations do |t|
t.string :street
t.string :house_number
t.string :zip_code
t.string :city
t.belongs_to :shop
end
But how to solve the uniqueness problem?
Another day, another undocumented Rails feature!
This time, it’s that ActiveRecord::Base.connection.add_index supports an undocumented option to pass a string argument as the v...
Rails: How to find records with empty associations
Imagine these models and associations:
class Deck < ApplicationRecord
has_many :cards
end
class Card < ApplicationRecord
belongs_to :deck, optional: true
end
Now you want to find all Decks without any Card or all Cards without a Deck.
Rails 6.1+
Rails 6.1 introduced a handy method ActiveRecord#missing to find records without given associations.
Deck.where.missing(:cards)
SELECT "decks".*
FROM "dec...
How to debug file system access in a Rails application
It might sometimes be useful to check whether your Rails application accesses the file system unnecessarily, for example if your file system access is slow because it goes over the network.
The culprit might be a library like carrierwave that checks file existence or modification times, whereas your application could determine all this from your database.
Introducing strace
One option it to use strace for this, which logs all system calls performed by a process.
To do this, start your rails server using something like
DISA...
Capybara: Most okayest helper to download and inspect files
Testing file download links in an end-to-end test can be painful, especially with Selenium.
The attached download_helpers.rb
provides a download_link
method for your Capybara tests. It returns a hash describing the download's response:
details = download_link('Download report')
details[:disposition] # => 'attachment' or 'inline'
details[:filename] # => 'report.txt'
details[:text] # => file content as string
details[:content_type] # => 'text/plain'
Features
Compared to [other approaches](...
Use DatabaseCleaner with multiple test databases
There is a way to use multiple databases in Rails.
You may have asked yourself how you're able to keep your test databases clean, if you're running multiple databases with full read and write access at the same time. This is especially useful when migrating old/existing databases into a new(er) one.
Your database.yml
may look like this:
default: &default
adapter: postgresql
encoding: unicode
username: <%= ENV['DATABASE_USER'] %>
host: <%= ENV['DATABASE...
ActiveRecord: Query Attributes
tl;dr
You can useattribute?
as shorthanded version ofattribute.present?
, except for numeric attributes and associations.
Technical Details
attribute?
is generated for all attributes and not only for boolean attributes.
These methods are using #query_attribute
under the hood. For more details you can see ActiveRecord::AttributeMethods::Query
.
In most circumstances query_attribute
is working like attribute.present?
. If your attribute is responding to :zero?
then you have to be aware that `query_attri...