When storing floating-point numbers such as prices or totals in an SQL database, always use a DECIMAL column. Never use FLOAT or kittens will die.

DECIMAL columns are parametrized with a precision and a scale. These parameters describe which numbers can be stored in that column. E.g. a decimal with a precision of 5 and a scale of 2 can store numbers from -999.99 to 999.99, but not 1000 or 1.234.

This card explains what various databases do when you try to store a number in a DECIMAL field, and that number exceeds that colum...

If you save a non-standard object (not a String or Fixnum, etc) like the AwesomeClass from your application in the session of visitors be prepared that some time you will get this exception:

ActionController::SessionRestoreError: Session contains objects whose class definition isn't available. Remember to require the classes for all objects kept in the session. (Original exception: ...)

This happens when you remove your AwesomeClass but users come back to your site and still have the serialization of such objects in their session....

The Edge Rider gem will define a method collect_ids on your ActiveRecord models, scopes, integer scalars and collections, which will return a list of their IDs:

User.last.collect_ids # => [9]
[User.first, User.last].collect_ids # => [1, 9]
User.active.collect_ids # => [4, 5, 6]
[4, 5, 6].collect_ids # => [4, 5, 6]
7.collect_ids #=> [7]

This allows you to parametrize scopes with a variety of argument types:

class Note < ActiveRecord::Base
  named_scope :for_users, lamb...

ActiveRecord gives you the :include option to load records and their associations in a fixed number of queries. This is called preloading or eager loading associations. By preloading associations you can prevent the n+1 query problem that slows down a many index view.

You might have noticed that using :include randomly seems to do one of the following:

1. Execute one query per involved table with a condit...

Rails 3

User.active.to_sql

Rails 2

Use either the Edge Rider or fake_arel gem to get #to_sql backported to Rails 2.

If you don't want to use a gem for this, you can do this with vanilla Rails 2:

User.active.construct_finder_sql({})

Note: ActiveRecord::Base#becomes has a lot of quirks and inconsistent behavior. You probably want to use ActiveType.cast instead.

ActiveRecord models have with a method becomes(klass) which you can use to cast the record into an instance of its subclasses or superclass. This is useful because some parts of Rails reflect on the class of an instance, e....

Bryan talked about the differences between imperative and declarative scenarios. In my opinion, both styles have benefits and should be used appropriately based on the situation. The majority of examples on rspec's story runner currently on the web, including mine, are of the imperative type. Since the declarative type has many advantages I thought it would be worth while to present some examples and contrast the differences between the two styles.

When using ActionMailer, you can set an array of email addresses as recipients. If this array is generated by e.g. collecting email addresses from the database, it might sometimes be empty.

To prevent ActionMailer to deliver mails to nobody, simply overwrite the deliver! method like this:

# In your mailer.rb
def deliver!(mail = @mail)
  return false if (recipients.nil? || recipients.empty?) && (cc.nil? || cc.empty?) && (bcc.nil? || bcc.empty?)
  super
end

The information in this card is only relevant for Rails 2.3-era apps.

This note gives a quick introduction into caching methods (page caching, action caching and fragment caching) in rails and describes some specific problems and solutions.

The descriptions below are valid for Rails 2 and 3. Recently, caching with timestamp- or content-based keys has become more popular which saves you the pain of invalidating stale caches.

How to enable/disable caching

To enable or disable caching in rails you ca...

Sometimes you can make your life easier by not allowing a record attribute to be changed after the record was created. An example for this is when your model represents a child node in a composition and has logic that is hard to support for cases when the container changes.

Here is an example for a container Region composed of many children of type Holiday. After saving a Holiday it caches the current number of holidays in its region:

class Region < ActiveRecord::Base

...

ActiveRecord comes with a method touch which sets the updated_at timestamp to the current time. Unfortunately it also runs callbacks (and hence validations) on the receiving record, so it is unsuitable if you call it very often.

Use the attached initializer to get a touch_gently method which updates updated_at, but does not run callbacks:

User.find(5).touch_gently

The initializer will also give you a method touch_all_gently whi...

Specify these gem versions in your Gemfile:

gem 'cucumber', '~> 1.3.0'
gem 'cucumber-rails', '= 0.3.2' # max version for Rails 2
gem 'capybara', '< 2' # capybara 2+ requires Rails 3
gem 'mime-types', '< 2' # dependeny of capybara
gem 'nokogiri', '< 1.6' # dependency of capybara
gem 'rubyzip', '< 1' # dependency of selenium-webdriver, rubyzip 1+ requires Ruby 1.9
gem 'cucumber_factory'
gem 'database_cleaner', '< 1'
gem 'cucumber_spinner', '~> 0.2.5'
gem 'launchy', '~> 2.1.2'

With these versions set, `...

Sometimes you need to dynamically load an image and do something as soon as its loaded (when for example its size is already available).

With jQuery, this seems to work across browsers:

$('<img>')
  .attr('src', '')
  .load(function() {
    alert('fully loaded!');
  })
  .attr('src', '/the/real/image/url');

The shell variable PS1 holds your bash prompt. You might want to change it to serve your needs best. Here is how to:

General

• non-printing escape sequences in your prompt have to be inclosed in \[\e[ and \] so your shell can correctly count its prompt's length
• we recommend to highlight your prompt on production machines
• you can also [show different root prompts for each user](https://makandracards.com/makandra/9569-get-the-username-w...

Add deprecation warnings and their solution or link to available solutions.

Global access to Rake DSL methods is deprecated. Please include Rake::DSL into classes and modules which use the Rake DSL methods.

Open your Rakefile and add the following line above YourApp::Application.load_tasks:

YourApp::Application.class_eval do
  include Rake::DSL
end

Use of ole/file_system is deprecated. Use ole/storage (the file_system api is recommended and enabled by default)...

Pie sometimes does not properly redraw elements upon changes. This often happens when the change comes from somewhere further up the DOM.

Consider something like:

<ul>
  <li class="active"><div class="content">Active element</div></li>
  <li class="inactive"><div class="content">Inactive element</div></li>
</ul>

with CSS
li .content {
-webkit-box-shadow: #666 0px 2px 3px;
-moz-box-shadow: #666 0px 2px 3px;
box-shadow: #666 0px 2px 3px;
behavior: url(/PIE.htc);

  back...

JavaScript Garden is a growing collection of documentation about the most quirky parts of the JavaScript programming language. It gives advice to avoid common mistakes, subtle bugs, as well as performance issues and bad practices that non-expert JavaScript programmers may encounter on their endeavours into the depths of the language.

JavaScript Garden does not aim to teach you JavaScript. Former knowledge of the language is strongly recommended in order to understand the topics covered in this guide

The attached RSpec matcher exist_in_database checks if a given record still exists in the database and has not been destroyed:

describe Ticket do
  describe '.purge_expired' do
    fresh_ticket = Ticket.create(:expiry => Date.tomorrow)
    expired_ticket = Ticket.create(:expiry => Date.yesterday)
    Ticket.purge_expired
    fresh_ticket.should exist_in_database
    expired_ticket.should_not exist_in_database
  end
end

Note that there is also [ActiveRecord::Base#destroyed?](http://apidock.com/rails/ActiveRecord/Base/destroyed...

When you need to insert many records into the same table, performance may become an issue.

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 tried it out with a simple model and 500 iterations, the loop completed in 1.5 seconds vs. 6 seconds without a transaction.

Alternative

Another fast way to insert many ...

Depending on where you live, different rules are used to determine the number of the week and a weekday. You have no chance whatsoever to get this right globally unless you make it your life's purpose. However, when you work for clients from Europe or the US, there are two dominantish standards you should know about. Each of these has subtle differences.

ISO 8601

• This is adhered to by most European countries.
• Weeks start on Mon...

You can find ActiveRecord models by using a Range as its conditions:

User.scoped(:conditions => { :id => 3..5 })

This will generate the following query:

SELECT * FROM `users` WHERE (`users`.`id` BETWEEN 3 AND 5)

This also means that all your scopes that take an array of allowed values and use condition hashes, automagically work for Ranges, too.

In order to

• track down warnings and to see failing specs immediately
• or to get an overview of the core functionalities,

you can use RSpec's "nested" format. It looks like this:

Tool
  validations
    should require model to be set
    should require place_id to be set
  #identifier
    should include the model and tag if the tool has a tag
    should return the model if the tool has no tag
  .search
    should find tools by model and maker
    should find tools by serial number

Call RSpec like...