TL;DR: Bundler 2.0 will rename Gemfile to gems.rb and Gemfile.lock to gems.locked (sic).

The old filenames will be supported until the release of Bundler 3.0.

Some more breaking changes here.

RSpec allows defining methods inside describe/context blocks which will only exist inside them.
However, classes (or any constants, for that matter) will not be affected by this. If you define them in your specs, they will exist globally. This is because of how RSpec works (short story: instance_eval).

Negative example:

describe Notifier do
  class TestRecord < ApplicationRecord # DO NOT do this!
    # ...
  end
  
  let(:record) { TestRecord.new }
  
  it { ... }
end

# TestRecord will exist here, outside of the spec!

D...

There are several gems that make it easy to read and process xlsx files. Parsing the entire file at once however is error-prone since each cell is transformed to a ruby object - sometimes including thousands of formatted but empty cells.

As of today, I found two promising alternatives that provide a stream-based access to spradsheet rows:

• Roo supports multiple spreadsheet types like ODS or CSV and has a quite large contributor base
• [Creek](https://github.com/pythonicrubyis...

Summary

• Use return to return from a method. return accepts a value that will be the return value of the method call.
• Use break to quit from a block and from the method that yielded to the block. break accepts a value that supplies the result of the expression it is “breaking” out of.
• Use next to skip the rest of the current iteration. next accepts an argument that will be the result of that block iteration.

The following method will serve as an example in the details below:

def example
  puts yield
  puts ...

I frequently find myself needing a combination of group_by, count and sort for quick statistics. Here's a method on Enumerable that combines the three:

module Enumerable
  def count_by(&block)
    group_by(&block)
      .transform_values(&:count)
      .sort_by(&:last)
      .to_h
  end
end

Just paste that snippet into a Rails console and use #count_by now!

Usage examples

• Number of email addresses by domain:

> User.all.count_by { |user| user.email.sub /^.*@/, '' }
=> { "sina.cn"=>2, ..., "hotmail.com"=>128...

Scope is all about where something is visible. It’s all about what (variables, constants, methods) is available to you at a given moment. If you understand scope well enough, you should be able to point at any line of your Ruby program and tell which variables are available in that context, and more importantly, which ones are not.

The article gives detailed explanation on the variable scope in ruby with examples that are easy to understand. Every ruby developer should at least know the first part of the article by heart. The second half ...

You can use local copies of gems in your Gemfile like this:

gem 'spreewald', path: '~/gems/spreewald'

As soon as you have bundled your project with the local copy of the gem, all code changes in the copy will be available on your project. So you can for example set a debugger or add console output in the gem and use it from your project.
If you checked out the gem with your versioning tool, you can easily reset your changes afterwards or make a pull request for the gem if you improved it.

Don't commit a Gemfile with local path...

In the ruby shell (IRB) and rails console the return value of the previous command is saved in _ (underscore). This might come in handy if you forgot to save the value to a variable and further want to use it.

Example:

irb(main):001:0> 1 + 2
=> 3
irb(main):002:0> _
=> 3
irb(main):003:0> a = _
=> 3

I often see the use of || to set a default value for a variable that might be nil, null or undefined.

x = x || 'default-value'

This pattern should be avoided in all languages.

While using || works as intended when x is null or an actual object, it also sets the default value for other falsy values, such as false. false is a non-blank value that you never want to override with a default.

To make it worse, languages like JavaScript or Perl have [many more fal...

ActiveRecord::RecordNotFound errors provide quite meaningful error messages that can provide some insight on application details. Consider the following:

ActiveRecord::RecordNotFound: Couldn't find Organisation::Membership with 'id'=12 [WHERE "organisation_memberships"."user_id" = 1]

You should probably not simply render those error messages to the user directly. Instead you you might want to re-raise your own errors. ActiveRecord::RecordNotFound provides you with methods :model and :id where you can get information about w...

This card will show you a cool way to define a class using Struct.new.
A common usecase for Structs are temporary data structures which just hold state and don't provide behaviour. In many cases you could use a simple hash as a data structure instead. However, a Struct provides you with a nice constructor, attribute accessors and complains if you try to access undefined attributes. Structs are easy to compare (by attributes). A struct gives meaning to the data.

Disclaimer

Structs are great...

Nowadays it is fairly easy to intercept and modify mails globally before they are sent. All you have to do is register an interceptor class which responds to .delivering_email(message). This card will show you two common use cases.

Subject prefix:

Usually you want to prefix the subject line of emails with the current environment (except production) so you can differentiate between production mails and mails from other environments. Of course a...

Rails supports time zones, but there are several pitfalls. Most importantly because Time.now and Time.current are completely different things and code from gems might use one or the other.

Especially configuring an application that cares only about one time zone is a bit tricky.

The following was tested on Rails 5.1 but should apply to Rails 4.2 as well.

Using only local time

Your life will be easier if your application does not need to support time zones. Disable them like this:

config.time_zone = 'Berlin' # Your local ...

You can use gem list to list all gems available from a remote gem server:

gem list -r --clear-sources -s 'https://user:password@gemserver.tld/'

This is useful to debug cases where Bundler complains of a gem existing in more than one gem source.

Ruby's standard library is in the process of being gemified. It will soon - Ruby 2.5 - consist of RubyGems, which can be updated independently from Ruby.

This might mean smoother Ruby upgrades in the future. If breaking API changes happen in standard gems, we can update these before upgrading Ruby.

Middleman is a static page generator that brings many of the goodies that Rails developers are used to.

Out of the box, Middleman brings Haml, Sass, helpers etc. However, it can be configured to do even better. This card is a list of improvement hints for a Rails developer.

Gemfile

Remove tzinfo-data and wdm unless you're on Windows. Add these gems:

gem 'middleman-livereload'
gem 'middleman-sprockets' # Asset pipeline!

gem 'bootstrap-sass' # If you want to use Bootstrap

gem 'byebug'

gem 'capistrano'
gem 'capistrano-mid...

Dump this method into your Ruby console to quickly print data in columns. This is helpful for e.g. comparing attributes of a set of Rails records.

def tp(objects, *method_names)
  terminal_width = `tput cols`.to_i
  cols = objects.count + 1 # Label column
  col_width = (terminal_width / cols) - 1 # Column spacing

  Array(method_names).map do |method_name|
    cells = objects.map{ |o| o.send(method_name).inspect }
    cells.unshift(method_name)

    puts cells.map{ |cell| cell.to_s.ljust(col_width) }.join ' '
  end

  nil
end

Usag...

In case you want to require a gem, that is not in the Gemfile of you bundle and therefore not in your loadpath, you need to add the path manually and require the gem afterwards.

Expected error

Requiring a gem, that is not in the Gemfile or .gemspec, will cause an LoadError exception:

require 'example_gem' => LoadError: cannot load such file -- example_gem

Adding a gem to the loadpath temporary

1. You need to install the gem

gem install 'example_gem'

2. Then you need to require the path where the gem was install...

This card compares patterns to store trees in a relation database like MySQL or PostgreSQL. Implementation examples are for the ActiveRecord ORM used with Ruby on Rails, but the techniques can be implemented in any language or framework.

We will be using this example tree (from the acts_as_nested_set docs):

root
|
+-- Child 1
|   |
|   +-- Child 1.1
|   |
|   +-- Child 1.2
|
+-- ...

The parallel-gem is quite easy to use and can speed up rendering time if you want to render the same partial multiple times (e.g. for rendering long lists of things).
If your parallelized code talks to the database, you should ensure not to leak database connections.

Consider you want to render a list of groups with their members as json. You can use a partial for the rendering of group members, b...