Merging two arbitrary ActiveRecord scopes

(Rails has a method ActiveRecord::Relation#merge that can merge ActiveRecord scopes. However, its behavior has never been clear, and in Rails 7 it still discards conditions on the same column by the last condition. We discourage using #merge!)

The best way to merge ActiveRecord scopes is using a subquery:

scope_a.where(id: scope_b)

It is a little less concise than #merge, but unambiguous.

Example

Assume a model where a deal has many documents:

class Deal < ApplicationRecord
  has_many :...

Testing if two date ranges overlap in Ruby or Rails

A check if two date or time ranges A and B overlap needs to cover a lot of cases:

  1. A partially overlaps B
  2. A surrounds B
  3. B surrounds A
  4. A occurs entirely after B
  5. B occurs entirely after A

This means you actually have to check that:

  • neither does A occur entirely after B (meaning A.start > B.end)
  • nor does B occur entirely after A (meaning B.start > A.end)

Flipping this, A and B overlap iff A.start <= B.end && B.start <= A.end

The code below shows how to implement this in Ruby on Rails. The example is a class `Interv...

Zeitwerk: How to collapse folders in Rails

All direct child directories of app are automatically added to the eager- and autoload paths. They do NOT create a module for namespacing. This is intuitive, since there normally is no module Model, or module Controller. If you want to add a new base directory, there's no additional config needed.

Example

app
├── controllers
├── helpers
├── inputs # No config needed 
├── mailers
├── models
├── uploaders # No config needed
├── util # No config needed
└── workers # No config needed

Sometimes it's handy to group files wit...

How to: Upgrade CarrierWave to 3.x

While upgrading CarrierWave from version 0.11.x to 3.x, we encountered some very nasty fails. Below are the basic changes you need to perform and some behavior you may eventually run into when upgrading your application. This aims to save you some time understanding what happens under the hood to possibly discover problems faster as digging deeply into CarrierWave code is very fun...

Whitelists and blacklists

The following focuses on extension allowlisting, but it is the exact same thing for content type allowlisting with the `content_ty...

Google Chrome: How to restore the old downloads bar

The old Chrome downloads bar had several advantages over the new subtle downloads dropdown:

  • see all (many, at least) downloads at once and see their progress
  • downloads can be opened with a single click
  • drag them back into another web page to upload them again, with no extra clicks required

How to get it back

  1. Go to chrome://flags/#download-bubble
  2. Click the dropdown and change it to Disabled

They say the flag might be removed in the future, but for now it gets the downloads bar back.

Delivering Carrierwave attachments to authorized users only

Preparation

To attach files to your records, you will need a new database column representing the filename of the file. To do this, add a new migration (rails g migration <name>) with the following content:

class AddAttachmentToNotes < ActiveRecord::Migration[6.0]
  def change
    add_column :notes, :attachment, :string
  end
end

Don't forget to rename the class and change the column details to fit your purpose. Run it.

1) Deliver attachments through Rails

The first way is to store your Carrierwave attachments not ...

Geordi hints

Reminder of what you can do with Geordi.

Note: If you alias Geordi to something short like g, running commands gets much faster!
Note: You only need to type the first letters of a command to run it, e.g. geordi dep will run the deploy command.

geordi deploy

Guided deployment, including push, merge, switch branches. Does nothing without confirmation.

geordi capistrano

Run something for all Capistrano environments, e.g. geordi cap deploy

geordi setup -t -d staging

When you just clon...

Regular Expressions: Space Separators

Matching the "space" character class

For matching whitespaces in a regular expression, the most common and best-known shorthand expression is probably \s.
It matches the following whitespace characters:

  • " " (space)
  • \n (newline)
  • \r (carriage return)
  • \t (tab)
  • \f (form feed/page break)

However, in some cases these may not be good enough for your purpose.

Non-breaking spaces (nbsp)

Sometimes a text may contain two words separated by a space, but the author wanted to ensure that those words are written in the same lin...

Solving "TypeError (nil can't be coerced into Integer)" in the Rails console / IRB

On the Rails console, assigning an object to a variable can lead to this strange error (without stacktrace):

irb > recipient = Recipient.find(123)
Traceback (most recent call last):
TypeError (nil can't be coerced into Integer)
irb > recipient
#<Recipient ...

The error is only in the output – the assignment is working. It only occurs when using the --nomultiline option, and thus [only with IRB 1.2.0+ and before Ruby 3](https://github.com/makandra/geordi/blob...

PSA: Be super careful with complex `eager_load` or `includes` queries

TLDR

Using .includes or .eager_load with 1-n associations is dangerous. Always use .preload instead.

Consider the following ActiveRecord query:

BlogPost.eager_load(
  :comments
  :attachments,
).to_a

(Let's assume we only have a couple of blog posts; if you use pagination the queries will be more complicated, but the point still stands.

Looks harmless enough? It is not.

The problem

ActiveRecord will rewrite this into a query using LEFT JOINs which looks something like this:

SELECT "blog_posts...

Ruby: `extend` extends the singleton class's inheritance chain

In the discussion of the difference between include and extend in Ruby, there is a misconception that extend would add methods to the singleton class of a ruby object as stated in many posts on this topic. But in fact, it is added to the ancestors chain of the singleton class! Even though it is technically not the same, practically this can be considered the same in most use cases.

Example

This means, that we are able to overwrite these methods or call the parent version with super depending in which order and in whi...

Debug MiniMagick calls in your Rails app

Most of our applications use CarrierWave for file uploads. CarrierWave has an integrated processing mechanism for different file versions with support for ImageMagick through CarrierWave::MiniMagick (which requires the mini_magick gem). In case your processing runs into an error, CarrierWave will just swallow it and rethrow an error with a very generic message like Processing failed. Maybe it is not an image? which does not help you finding out what the actual problem is. CarrierWave probably does this for security purposes, but does n...

Heads Up: Selenium 4 uses a binary to determine the chromedriver

I recently stumbled over a problem that my feature tests broke in CI because of a mismatching chromedriver version.

In this specific project we have a fixed Chromium version in a Debian 12 environment instead of Chrome. The tests however used a recent chrome version instead.

$ chromedriver --version
ChromeDriver 117.0.5938.149 (e3344ddefa12e60436fa28c81cf207c1afb4d0a9-refs/branch-heads/5938@{#1539})
$ chromium --version
Chromium 117.0.5938.149 built on Debian 12.1, running on Debian 12.1

> WARN Selenium [:selenium_manager] The chromed...

Heads up: Quering array columns only matches equally sorted arrays

Given you have an array column like this:

create_table "users", force: :cascade do |t|
  t.integer "movie_ids", default: [], array: true
end

You might think that the following queries yield the same result:

User.where(movie_ids: [16, 17])
User.where(movie_ids: [17, 16])

Turn's out - they are not! They do care about array ordering more than I do.

To query for identical arrays independent of their order you have to either:

  1. Sort both the query and database content. If you're on Rails 7.1 you can use the new [`normal...

Ensure passing Jasmine specs from your Ruby E2E tests

Jasmine is a great way to unit test your JavaScript components without writing an expensive end-to-end test for every small requirement.

After we integrated Jasmine into a Rails app we often add an E2E test that opens that Jasmine runner and expects all specs to pass. This way we see Jasmine failures in our regular test runs.

RSpec

In a [feature spec](https://web.archive.org/web/20150201092849/http://www.rel...

Things you probably didn’t know you could do with Chrome’s Developer Console

Collection of useful tools in the Chrome JavaScript console.

Make the whole page editable

This is not special to Chrome, but still a clever thing:

document.body.contentEditable=true 

Taking time

You can easily measure the time on the console with named timers:

console.time('myTime'); // Start timer
console.timeEnd('myTime'); // End timer and print the time

Reference previously inspected elements (from the Elements panel)

Variables $0, $1, ... $n reference the nth-last inspected Element. $0 ...

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...

Parallelize Development Using Git Worktrees

You can use git worktree to manage multiple working trees attached to the same repository. But why should I use git worktree?

You can use more than one working tree to ...

... run tests while working on another branch
... compare multiple versions
... work on a different branch without disturbing your current branch

Creating a new working tree is as simple as creating a new branch. You only need to execute git worktree add <path> <branch>. When you are done, you can remove the working tree with git worktree remove <Worktree>...

Carrierwave: Deleting files outside of forms

TL;DR Use user.update!(remove_avatar: true) to delete attachments outside of forms. This will have the same behavior as if you were in a form.


As you know, Carrierwave file attachments work by mounting an Uploader class to an attribute of the model. Though the database field holds the file name as string, calling the attribute will always return the uploader, no matter if a file is attached or not. (Side note: use #present? on the uploader to check if the file exists.)

class User < ApplicationRecord
  mount :avatar, ...

Use Time.current / Date.current / DateTime.current on projects that have a time zone

Basically, you now need to know if your project uses a "real" time zone or :local, and if config.active_record.time_zone_aware_attributes is set to false or not.

  • With time zones configured, always use .current for Time, Date, and DateTime.

    ActiveRecord attributes will be time-zoned, and .current values will be converted properly when written to the database.
    Do not use Time.now and friends. Timezone-less objects will not be converted properly when written to the database.

  • With no/local time zone use Time.now, `...

RSpec: Leverage the power of Capybara Finders and Matchers for view specs

View specs are a powerful tool to test several rendering paths by their cases instead of using a more costing feature spec. This is especially useful because they become quite convenient when used with Capybara::Node::Finders and Capybara::RSpecMatchers. This allows to wirte view unit specs as you can isolate specific part...

RSpec: Ensuring a method is called on an object that will be created in the future

rspec >= 3.1 brings a method and_wrap_original. It seems a bit complicated at first, but there are use cases where it helps to write precise tests. For example it allows to add expectations on objects that will only be created when your code is called.

If you have older rspec, you could use expect_any_instance_of, but with the drawback, that you can't be sure if it really was the correct instance which got the message.

Example

The example model uses different validators based on a flag:

class MyModel < ApplicationRecord

 ...

Whenever: Don't forget leading zeros for hours!

Whenever is a Ruby gem that provides a nicer syntax for writing and deploying cron jobs.

Leading zeros are important for whenever if you use the 24-hours format!

This schedule.rb:

every 1.day, at: '3:00', roles: [:primary_cron] do
  runner 'Scheduler.delay.do_things'
end

will lead to this crontab entry (crontab -l) with the default configuration:

0 15 * * * /bin/bash -l -c 'cd /var/www/my-project/releases/20180607182518 && bin/rails runner -e production '\''Scheduler.delay.do_things'\'''

Which would run on 3...

Heads up: RSpec's diffs may not tell the truth

RSpec provides a nice diff when certain matchers fail.

Here is an example where this diff is helpful while comparing two hashes:

{a:1}.should match(a:1, b:2)

Failure/Error: {a:1}.should match(a:1, b:2)
  expected {:a=>1} to match {:a=>1, :b=>2}
  Diff:
  @@ -1,3 +1,2 @@
   :a => 1,
  -:b => 2,

Unfortunately, this diff is not as clever as it would need to. RSpec's instance_of matchers will look like errors in the diff (even if they are not), and time objects that differ only in milliseconds won't appear in the ...