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Repeats

Tod: A Gem for handling daytime without a date

Tod is a gem for working with daytimes.

Another additional gem?

Thus SQL has a time datatype for storing time of day in the format hh:mm:ss, neither Ruby nor Rails themselves offer an elegant way to deal with day times.

Time and DateTime both handle daytime values AND calendar date, using them to only store the time of day will end in inconsistent and thus confusing data, e. g. Time.new will initialize with the current Time in your Timezone, DateTime.new initializes at January 1, at an undefined year, without a timezone o…

Repeats

When reading model columns during class definition, you must handle a missing/empty database

When doing some meta-programming magic and you want to do something for all attributes of a class, you may need to access connection or some of its methods (e.g. columns) during class definition.

While everything will be fine while you are working on a project that is in active development, the application will fail to boot when the database is missing or has no tables. This means that Raketasks like db:create or db:migrate fail on a freshly cloned project.

The reason is your environment.rb which is loaded for Raketasks and calls…

Migration from the Asset Pipeline to Webpacker

This is a short overview of things that are required to upgrade a project from the Asset Pipeline to Webpacker. Expect this upgrade to take a few days even the diff is quite small afterwards.

Preparations

1. Find all libraries that are bundled with the asset pipeline. You can check the application.js and the application.css for require and import statements. The source of a library is most often a gem or a vendor directory.
2. Find an working example for each library in the application and write it down.
3. Find out the ver…

Linked content

MySQL: How to create columns like "bigint" or "longtext" in Rails migrations, and what :limit means for column migrations

Rails understands a :limit options when you create columns in a migration. Its meaning depends on the column type, and sometimes the supplied value.

The documentation states that :limit sets the column length to the number of characters for string and text columns, and to the number of bytes for binary and integer columns.

Using it

This is nice since you may want a bigint column to store really long numbers in it. You can just create it by …

Repeats

Authorize allowed values with assignable_values

All our projects have enum-like requirements like this:

  • An attribute value must be included in a given set of values.
  • The list of allowed values must be retrievable in order to render <select> boxes.
  • Each value has a humanized label.
  • Sometimes there is a default value.

Most of the time, this requirement is also needed:

  • The list of assignable values depends on the user who is currently signed in.

In our past projects there are many different solutions for these related requirements, e.g. ChoiceTrait, methods like `available_…

Linked contentRepeats

Databases don't order rows unless you tell them so

There is no such thing as a "default order" of rows in database tables.

For instance, when you paginate a result set: When using LIMIT, it is important to use an ORDER BY clause that constrains the result rows into a unique order. Otherwise you will get an unpredictable subset of the query's rows. You might be asking for the tenth through twentieth rows, but tenth through twentieth in what ordering? The ordering is unknown, unless you specified ORDER BY.

In Rails, if you use Record.first or Record.last, it will default to orderin…

Repeats

Enumerators in Ruby

Starting with Ruby 1.9, most #each methods can be called without a block, and will return an enumerator. This is what allows you to do things like

['foo', 'bar', 'baz'].each.with_index.collect { |name, index| name * index }
# -> ["", "bar", "bazbaz"]

If you write your own each method, it is useful to follow the same practice, i.e. write a method that

  • calls a given block for all entries
  • returns an enumerator, if no block is given

How to write a canonical each method

To write a metho…

Repeats

How to Work With Time Zones in Rails

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…

Why you can't use timezone codes like "PST" or "BST" for Time objects

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) …

Repeats

Custom error pages in Rails 3.2+

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…

Repeats

MySQL: Creating many records works faster in a transaction

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…

How to fix parallel_tests with Redis on powerful machines

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…

Repeats

Shortcut for getting ids for an ActiveRecord scope

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)
Repeats

MySQL: Careful when using database locks in transactions

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…

How to fix: Session hash does not get updated when using "merge!"

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…

Repeats

Do not rescue inline in Ruby

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...
Repeats

How to tackle complex refactorings in big projects

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…

Upgrade guide for moving a Rails app from Webpack 3 to Webpack 4

Webpacker is Rails' way of integrating Webpack, and version 4 has been released just a few days ago, allowing us to use Webpack 4.

I successfully upgraded an existing real-world Webpack 3 application. Below are notes on everything that I encountered.
Note that we prefer not using the Rails asset pipeline at all and serving all assets through Webpack for the sake of consistency.

Preparations

  • Remove version locks in Gemfile for webpacker
  • Remove version locks in package.json for webpack and webpack-dev-server
  • Install by ca…
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