If you have any class which requires access to some path methods generated by your routes. Even though you could technically include Rails.application.routes.url_helpers, this may include way too many methods and even overwrite some class methods in the worst case.

Instead, most of the time the following is advised to only make the desired methods available:

class Project
  delegate :url_helpers, to: 'Rails.application.routes'

  def project_path
    url_helpers.project_path(self)
  end
end

While it might seem trivial to implement an invoice that sums up items and shows net, gross and vat totals, it actually involves a lot of rules and caveats. It is very easy to create invoices where numbers don't add up and a few cents are missing. A missing cent is a big deal for an accountant, so it is important for your invoices to list correct numbers.

Note that this is not legal advice. Also note that while this note has a number of code examples in Ruby and MySQL, the concepts apply to all programming languages and data stores.

When ...

You've been there: A form cannot be submitted, but you don't see a validation error because the field at fault has no corresponding input field on the form. Because this is usually a bug, you insert debug information listing all errors into the form view. And once the bug is fixed, you forget to take out that debug information.

There is a better way. By copying one of the attached initializers into config/initializers, your forms will always render a small box listing all form errors in the bottom right corner of the screen. This box is n...

Calling Time#utc, Time#gmt or Time#localtime will not create a converted copy. Instead these methods modify the receiving Time object:

 >> time = Time.now
 => Thu Aug 25 09:52:28 +0200 2011
 >> time.utc
 => Thu Aug 25 07:52:28 UTC 2011
 >> time
 => Thu Aug 25 07:52:28 UTC 2011

This can have unexpected side effects when other code is holding pointers to the Time object you are modifying. To be safe, call these methods on a clone of the Time object. You can clone a Ruby object by using [#dup](http://...

I recently browsed through the ActiveSupport code and found some nice stuff I did not know about:

ActiveSupport::Callbacks

ActiveRecord-like callbacks, if you need callbacks in non ActiveRecord objects

ActiveSupport::MessageEncryptor

encrypt and decrypt ruby objects

[ActiveSupport::MessageVerifier](https://github.com/rails/rails/blob/mast...

When the Ruby parser module of Ruby-GetText comes across a file in one of its search directories (e.g. lib/scripts/) and finds out that you are defining ActiveRecord classes inside it, it evaluates the whole file. Here is how to avoid that.

What's happening?

Let's say you have the following script which is only run once, manually, via script/runner:

# lib/scripts/doomsday.rb
class User < ActiveRecord::Base; end
User.destroy_all

In that case we ...

Date::Performance is a gem that replaces various method in Ruby's Date class with fast C implementations. Unfortunately it doesn't fully implement an internal method (Date.ajd_to_jd) which makes your code blow up when you use it together with the Spreadsheet gem.

A solution is to restore the Ruby implementation of this particular method. To do this, copy the attached file to lib/fix_date_performance.rb to config/initializers.

When your Cucumber feature needs to browse the page HTML, and you are not sure how to express your query as a clever CSS or XPath expression, there is another way: You can use all and find to grep through the DOM and then perform your search in plain Ruby.

Here is an example for this technique:

Then /^I should see an image with the file...

When you need to create a locale for a language variant (like Austrian for German), you probably don't want to duplicate your entire de.yml file only to change a few minor exceptions for our Austrian friends.

Luckily, the I18n gem used by Rails has a fallback feature where you can make one locale file fall back to another if no translation is available.

In the example above you would have a config/locales/de_DE.yml:

de_DE:
  # hundreds of translations here

... and another...

When you need to use diff in either some Ruby code or your Rails app, use the differ gem.

puts Differ.diff "foo", "boo"
# => {"boo" >> "foo"}

Usage

There are several variants available, all using the base method diff(to, from, separator = "\n").
You have diff_by_line, diff_by_word, diff_by_char and may of course use your own separator:

puts Differ.diff 'Hauptsatz, und mein Nebensatz.', 'Hauptsatz, und dein Nebensatz.', ','
# => Hauptsatz,{" und dein Nebensatz." >> " un...

When you need to zip up files in Ruby, use zipruby.

sudo gem install zipruby

You can add existing files, add files from strings and even add directories.
Example usage:

require 'zipruby'
cars = %w[audi bmw mercedes]

zipfile = Tempfile.new('my.zip', 'tmp')
Zip::Archive.open(zipfile.path, Zip::CREATE) do |zip|
  zip.add_file '/tmp/me.txt'
  zip.add_dir 'cars' 

  cars.each do |car|
    zip.add_buffer "cars/#{car}.txt", "This #{car} is mine!" 
  end
end

Credits go to winebarrel for the Ruby bin...

To offer files for download, use send_file.

def download(file)
  send_file file.path, :disposition => 'attachment'
end

Note that a send_file replaces the default :render action.

This is now part of geordi. Please don't follow the instructions below, if you use geordi.

Inspired by the recent headless Selenium note, I found yet another solution for the problem to hide your selenium tests away.

This has the advantages
^

• not to require a gem (so you do not force this on others)
• to allow you to take a look at the running webdriver if necessary

Simply make a script th...

Note: If you are currently working with Ruby 1.8.7 or 1.9.3, we recommend to upgrade to Ruby 2.1 first. From our experience this upgrade is much smoother than the jump from 2.1 and 2.2, while still giving your the huge performance gains of Ruby 2. Also, if you're on Ruby 1.8.7, we recommend to skip a troublesome upgrade to 1.9.3 and go straight to 2.1.

When trying to make a Rails app run on Ruby 1.9, you're likely to encounter several issues. Here are a few solutions (obviously not exhaustive):

When running `bundle ...

You can say

File.chmod(0604, '/path/to/file') # rw----r--

The leading zero is meaningful.

If you use Selenium and Launchy to open web pages, you might run into an error saying "Your Firefox profile cannot be loaded. It may be missing or inaccessible.".

This happens because Launchy tries to use your Firefox running the web driver to open the page.

For Launchy < 0.4.x, as a workaround you can set an environment variable

export LAUNCHY_BROWSER=`which google-chrome`

For newer Launchys you also need to set:

export BROWSER=`which google-chrome`

If you want to do this in a ruby script, you can say

chrome_path ...

API breakage ahoy. You need to either upgrade your Capybara or downgrade your selenium-webdriver gem.

Alternatively, this could solve your trouble.

Sometimes you need a file of some size (possibly for testing purposes). On Linux, you can use dd to create one.

Let's say you want a 23 MB file called test.file. You would then run this:

dd if=/dev/zero of=test.file bs=1048576 count=23

The block size (bs) is set to 1 MB (1024^2 bytes) here, writing 23 such chunks makes the file 23 MB big.\
Adjust to your needs.

This linux command might also come in handy in a Ruby program. It could be used like:

mb = 23
mb_string, _error_str, _status = Open3.capture3('dd if=/dev/zero...

We are changing our name from Hoptoad to Airbrake. You see, some folks much larger than us reached out and claimed trademark over all things related to frogs and toads and little animals of that ilk. After speaking to our lawyers we reluctanctly decided it’s best to change the name.

With gem dependency it is possible to check the dependencies for your gem before you install it.

Here is an example output for Nokogiri:

Gem nokogiri-1.4.4
  hoe (>= 2.6.2, development)
  minitest (>= 1.6.0, development)
  racc (>= 0, development)
  rake-compiler (>= 0, development)
  rexical (>= 0, development)
  rubyforge (>= 2.0.4, development)

Regular expressions can have something called "zero-width look-behind assertions". This means that you want a pattern to be preceded by another pattern, but not include the preceding pattern in your match or search cursor. E.g. (?<=x)y matches y in xyz but not in syz. There are also negative look-behind assertions, e.g. (?<!x)y matches y in syz but not in xyz.

Unfortunately look-behind assertions are only available in Ruby 1.9. With Ruby 1.8 you need to use an alternative regular expression library called [Oniguruma](http://...