CarrierWave: Processing images with libvips
When you write your next CarrierWave uploader, consider processing your images with libvips instead of ImageMagick.
Reasons for libvips
There are several upsides to using libvips over ImageMagick:
- libvips is considerably faster and uses less memory.
- ImageMagick has a large attack surface that has repeatedly caused security incidents in the past (compare [ImageMagick CVEs](https://www....
RubyMine and Rubocop: Performing safe autocorrects on save
- Ctrl + Alt + S > search "rubocop on save"
- Under "Inspections", check the highlighted box on
rubocop -a
Caveat: This adds a little time overhead to saving. When you're editing many files at once (e.g. using "Replace All"), this may be inacceptable.
Balance your texts today with text-wrap: balance
So you have a heading that is just barely wider than the container it should fit into, and it wraps a single word to a new line and it's not really pretty?
Cry no more, for you can use text-wrap: balance today to fix that. At least in some browsers.
When browsers encounter a text-wrapping element with text-wrap: balance style, they will try breaking to a new line sooner, if it balances out the width of lines.
text-wrap: unset |
text-wrap: balance |
|---|---|
| 
- A specific package has a bug in a more recent version
- You want to ensure no...
Capo: putting <head> content into the right order
How you order elements in the <head> can have an effect on the (perceived) performance of the page.
This script helps you identify which elements are out of order.
Also available as a Chrome Extension. It shows the actual order of head elements, and suggests an optimal order for page performance.
How to pretty print all values in a Redis database
With this Ruby script you can print all values in a Redis database to your console (derived from this bash script).
Note: Do not run this command in production. This is for debugging purposes only.
def pretty_print_redis(redis)
redis.keys.each_with_object({}) do |key, hash|
type = redis.type(key)
hash[key] = case type
when 'string'
redis.get(key)
when 'hash'
redis.hgetall(key)
when 'list'
redis.lrange(key, 0, -1)
when 'set'
redis.smembers(...
Better HTML forms: use type, inputmode, enterkeyhint and autocomplete
Web forms can be made much more usable with a few HTML attributes. Short summary:
The numericality validator does not care about your BigDecimal precision
Looking at the source code of the validates_numericality_of validator, it becomes clear that it converts the attribute in question to either an integer or float:
if configuration[:only_integer]
unless raw_value.to_s =~ /\A[+-]?\d+\Z/
record.errors.add(attr_name, configuration[:message] || ActiveRecord::Errors.default_error_messages[:not_a_number])
next
end
raw_value = raw_value.to_i
else
begin
raw_value = Kernel.Float(raw_val...
Preventing users from uploading malicious content
When you allow file uploads in your app, a user might upload content that hurts other users.
Our primary concern here is users uploading .html or .svg files that can run JavaScript and possibly hijack another user's session.
A secondary concern is that malicious users can upload executables (like an .exe or .scr file) and use your server to distribute it. However, modern operating systems usually warn before executing files that were downloaded from t...
Rails: Fixing ETags that never match
Every Rails response has a default ETag header. In theory this would enable caching for multiple requests to the same resource. Unfortunately the default ETags produced by Rails are effectively random, meaning they can never match a future request.
Understanding ETags
When your Rails app responds with ETag headers, future requests to the same URL can be answered with an empty response if the underlying content ha...
Jasmine: Preventing unhandled promise rejections from failing your test
You have an async function that rejects:
async function failingFunction() {
throw new Error("Something went wrong")
}
When you call that function in a test, your test will fail:
it('has a test', function() {
failingFunction() // this will fail your test
})
The failure message will look like this:
Unhandled promise rejection: Error: Something went wrong
You can fix this by expecting the state of the returned promise:
it('has a test', async function() {
await expectAsync(failingFunction()).toBeRej...
ActiveRecord::Relation#merge overwrites existing conditions on the same column
In Ruby on Rails ActiveRecord::Relation#merge overwrites existing conditions on the same column. This may cause the relation to select more records than expected:
authorized_users = User.where(id: [1, 2])
filtered_users = User.where(id: [2, 3])
authorized_users.merge(filtered_users).to_sql
# => SELECT * FROM users WHERE id IN (2, 3)
The merged relation select the users (2, 3), although we are only allowed to see (1, 2). The merged result should be (2).
This card explores various workarounds to combine two scopes so t...
Understanding database Indexes in PostgreSQL
I found the linked article very helpful to refresh my understanding of database indexes. As a small bonus, it includes a few helpful SQL oneliners like these two:
Warning
Do not run random code snippets unless you understand them in detail - especially in production.
How Haml 6 changes attribute rendering, and what to do about it
Haml 6 was a major rewrite with performance in mind. To achieve a performance improvement of 1.7x, some design trade-offs had to be made. The most notable change might be the simplified attribute rendering.
In Haml 5, attribute rendering knew two special cases: an attribute with value true would be rendered without a value, an attribute with a falsy value would not be rendered at all. All other values would just be rendered as attribute values.
According to the Haml maintai...
Simple Form: Rendering errors without an appropriate attribute
Usually you add errors to :base in ActiveRecord, in case no appropriate attribute could be used to add the error.
Simple Form doesn't render errors on :base by default, but here a few options how you can render these on demand. For all the options below we use the following example with a Simple Form Bootstrap configuration:
- @user = Backend::User.new
- @user.errors.add(:base, 'First error')
- @user.errors.add...
Rails: Assigning associations via HTML forms
Let's say we have posts with an attribute title that is mandatory.
Our example feature request is to tag these posts with a limited number of tags. The following chapters explain different approaches in Rails, how you can assign such an association via HTML forms. In most cases you want to use Option 4 with assignable values.
The basic setup for all options looks like this:
config/routes.rb
Rails.application.routes.draw do
root "posts#index"
resources :posts, except: [:show, :destroy]
end
**db/migrate/...
Beware when using ActiveSupport time and date calculation methods
The pitfall
Rails Active Support provides some helpful methods for calculating times and dates, like Duration#ago or Duration#from_now. But beware when using those, because they wont give you Dates or Times but ActiveSupport::TimeWithZone instances. As the class name hints, you now have to be awa...
Rails: Composing an ETag from multiple records
Rails offers the fresh_when method to automatically compute an ETag from the given record, array of records or scope of records:
class UsersController < ApplicationController
def show
@user = User.find(params[:id])
fresh_when @user
end
def index
@users = User.all.to_a
fresh_when @users
end
end
When your view also displays other records (typically associations), those other records should be included in the ETag. You can do so by passing an array of ETaggable objects to fresh_when.
...
Rails: Your index actions probably want strict_loading
By activating strict_loading you force developers to address n+1 queries by preloading all associations used in the index view. Using an association that is not preloaded will raise an ActiveRecord::StrictLoadingViolationError.
I think it's a good default to activate strict_loading in your controllers' #index actions. This way, when a change introduces an n+1 query, you...
Rails migration: Changing a column type without losing the content
The change_column method for rails migrations support casting with a custom SQL statement. This allows us to change a column type and keep the former content as the new type. This way, we can for example prepare an address number column to hold German address numbers, which can contain letters:
Example (in most cases not a good idea!)
class ChangeAnIntegerColumnToString < ActiveRecord::Migration[6.1]
def up
change_column :users, :address_number, 'varchar USING CAST(rating AS varchar)'
end
def down
change_column ...
Issue Checklist Template
This is a checklist I use to work on issues. For this purpose I extracted several cards related to the makandra process and ported them into a check list and refined that over time a little bit.
This task list is divided by the Gate keeping process in the following steps:
1. Starting a new feature
2. Working on the issue
3. Finishing a feature
4. After Review
Here are some ti...
Rails Partials
Rails partials have a lot of "hidden" features and this card describes some non-obvious usages of Rails Partials.
Rendering a basic partial
The most basic way to render a partial:
render partial: 'partial'
This will render a _partial.html.erb file. Notice how all partials need to be prefixed with _.
It's possible to define local variables that are only defined in the partial template.
# _weather.html.erb
<h1>The weather is <%= condition %></h1>
# index.html.erb
render partial: 'weather', locals: { condition: ...
Rails: Using database default values for boolean attributes
In the past we validate and set default values for boolean attributes in Rails and not the database itself.
Reasons for this:
- Older Rails didn't support database defaults when creating new records
- Application logic is "hidden" in the database
An alternative approach, which currently reflects more the general opinion of the Rails upstream on constraints in the database, is adding default values in the schema of the database itself. We also ...