With different time zones

When dealing with time zones in Rails, there is one key fact to keep in mind:

Rails has configurable time zones, while
Ruby is always in the server's time zone

Thus, using Ruby's time API will give you wrong results for different time zones.

For consistency, you should only use Rails' methods, but the hard thing is to know which method originates from Ruby and which from Rails. To simplify this, adhere to the following suggestion:

Use Time.zone for everything time-related

```
# Examp…

Rails' ActiveSupport::TimeWithZone objects have both a timezone code and offset, e.g. Thu, 28 Mar 2019 16:00:00 CET +01:00. Ruby's stdlib TZInfo also has time zones, but with different identifiers.
Unfortunately, not all timezone codes can be used to parse strings or to move time objects into another time zone.

Some timezone codes like CET are supported by ActiveSupport extensions like String#in_time_zone, while many codes will actually not work:

``` » '2019-03-01 12:00'.in_time_zone('PST')
ArgumentError (Invalid Timezone: PST) …

Starting with Rails 3.2, there is a nicer way to display custom error pages (i.e. "page not found") that does not interfere with ExceptionNotifier. (I'm not sure about Airbrake et al.)

José Valim has posted this on his blog, here is a slightly more verbose rundown:

1. Register your own app as the application responsible for showing error pages by adding

   config.exceptions_app = self.routes
   

   to your config/application.rb.

2. Add rout…

Reverting a commit means creating a new commit that undoes the old changes.

git revert commit_sha1

When you need to insert many records into the same table, a fast way to do it is to have a single INSERT statement describing multiple rows. Unfortunately there is no way to do this through ActiveRecord.

What you can do to save time is to open a transaction and save multiple records within that transaction:

transaction do
  500.times { Model.create! }
end

Although you will still trigger 500 INSERT statements, they will complete considerably faster.

When I trie…

min-width is known as a CSS property that can be set to define a least width for an element. Surprisingly, it can also be used to set something that feels like max-width.

min-width in a flex context

While the default min-width value is 0 (zero), for flex items it is auto. This can make block elements take up much more space than desired, even stretching their container beyond the screen edge on small screens.

[…

When we want to use our own (or bought) fonts in an application with Webpack(er), we have two options. We can

• put the fonts directly into your Webpack's assets folder or
• write an npm package with an own sass file that can be imported from the Webpack manifest.

Load fonts from your assets folder

The first option turns out to be straightforward: Import the stylesheets in the index.js of the pack you're using:

```javascript
// webpack_source_path/application/index.js

import './stylesheets/reset'
import…

Fixed bugs where calling valid? would change the record's state.

When you have a powerful machine with many CPU cores, you might run into an error like

ERR DB index is out of range (Redis::CommandError)

This is because Redis defaults to at most 16 databases (0 to 15) and running tests in parallel might exceed that (your tests might run on databases 1..n or 2..(n+1)).

You can increase that limit:

1. Get number of CPUs of your machine.

   nproc --all
   

2. Open up Redis configuration file.

   sudo vim /etc/redis/redis.conf
   

3. Find databases row and increase it, e.g. set to CPU cou…

You can use .ids on an ActiveRecord 4+ scope to pluck all the ids of the relation

User.where("users.name LIKE 'Foo Bar'").ids

# same as
User.where("users.name LIKE 'Foo Bar'").pluck(:id)

We tend to use database transactions as a magic bullet to get rid of all our concurrency problems. When things get really bad, we might even throw in some locking mechanism, but then are usually done with it.

Unfortunately, transactions semantics in databases are actually very complicated, and chances are, your making some incorrect assumptions.

The MySQL innodb engine actually has [four different modes](ht…

tl;dr: Do not use merge! for session hashes. Use update instead.

Outline

Let's assume you're modifying the Rails session. For simplicity, let's also assume your session is empty when you start (same effect when there is data):

# In our example, we're in a Rack middleware
request = Rack::Request.new(env)
request.session.merge! :hello => 'Universe'
request.session
=> {}

Wat?

Even worse: When you inspect your request.session like above (e.g. in a debugger shell, o…

When you are calling a method that may raise an exception that you don't care about, you might think of doing something like this:

@user = User.power_find(something) rescue User.new

Do not do that! You will be rescuing away StandardError and all its subclasses, like NameError – meaning that even a typo in your code won't raise an error.

Instead, rescue the exception type that you are expecting:

@user = begin
  User.power_find(something)
res...

Here is how to make Rome datepicker look like the rest of your Bootstrap 4 application.

Rome comes with very little basic styling. While we could redefine its classes, we can configure the classes Rome applies to its elements to make it look like this:

Since Bootstrap 4 comes with several helpful utility classes, and requires fewer markup/containers, we can achieve Bootstrap 4 experience by applying a few classes via the styles setting.

You still need to include `ro…

From at least Rails 4, the ActionView tag helper turns Array values of HTML options into a single space-separated string.
This means you can pass an array to :class options:

```
extra_classes = %w[one two]

= link_to 'Dashboard', root_path, class: ['btn', 'btn-primary', *extra_classes]
=> Dashboad

= content_tag 'div', 'Hello World', class: %w[alert alert-info]
=> <div class="alert alert-info">Hello World</div>

= …

So you want to use object-fit, but you also need to support Internet Explorer.

One option is to use lazysizes as a kinda-polyfill. Another option is to implement the requirement with background-size: contain, and background-size: cover, which is supported in IE9+.

E.g. to make an image cover a 100x100 px² area, cropping the image when nece…

Sometimes huge refactorings or refactoring of core concepts of your application are necessary for being able to meet new requirements or to keep your application maintainable on the long run. Here are some thoughts about how to approach such challenges.

Break it down

Try to break your refactoring down in different parts. Try to make tests green for each part of your refactoring as soon as possible and only move to the next big part if your tests are fixed. It's not a good idea to work for weeks or months and wait for ALL puzzle pieces to…