Apache HTTP server benchmarking tool (ab) is a nice tool to test performance on sites delivered by HTTP. If the site you're about to test is placed behind a login, follow these steps to successfully use ab on it.

1. Open the site to test in the browser of your choice. Do not login yet.
2. Use developer tools to show all cookies used by the site. (Chrome: Ctrl+Shift+i, open the 'Resources' tab and click on the site below 'Cookies' on the left. Firefox: Right-click on the site, open 'We...

In case you have sensitive data within your RDS instance, you want to use encrypted connections between your application and RDS instances. If you're using MySQL on RDS, here's what to do:

1. Download the AWS CA file and copy it to the machine you want to connect from: http://s3.amazonaws.com/rds-downloads/mysql-ssl-ca-cert.pem
   As far as I could find out, you (currently) cannot access further details of the SSL configuration (such as public key).

2. Try to connect using MySQL client

   `% mysql -uyour_username -p -h rds_hostname_from_...

When writing a piece of reusable code, you sometimes need to have separate code for Rails 2 and Rails 3. You can distinguish between Rails versions like this:

if Rails.version < '3' # mind the quotes
  # Rails 2 code goes here
else
  # Rails 3+ code goes here
end

Say we want …

• to create a Gallery that has a name and has_many :images, which in turn have a caption
• to offer the user a single form to create a gallery with any number of images
• immediate uploads with a progress bar per image
• a snappy UI

Enter jQuery File Upload. It's a mature library that can do the job frontend-wise. On the server, we'll use Carrierwave, because it's capable of caching images.

(FYI, [here's how to do the u...

With puma you can have concurrent requests. There are two concepts on how Puma can handle two incoming requests: Workers and Threads.

Workers

Puma can have multiple workers. Each worker is a process fork from puma and therefore a very heavy instance and can have multiple threads, that handle the incoming requests.

Example: A Puma server with 2 workers and 1 thread each can handle 2 request in parallel. A third request has to wait until the thread of one of the workers is free.

Threads

Rails is thread-safe since version 4 (n...

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...

It sometimes happen that a database dump, that would want to insert into your development database, does not match the current schema of the database. This often happens when you have an old dump, but your current setup is up to date with the the master.

Hint: In most cases it is sufficient to delete and recreate the local database in order to import the dump. If any problems occur, proceed as follows:

1. Figure out the original migration status of the dumpfile

• Convert your dump to plaintext: `pg_restore -f some.dump > some.dump....

When using send_file (for example for attachments of any kind), make sure your application knows the correct mime types so that all browsers can handle the files. It is much more convenient for users if they can decide to open a file directly instead of having to save it first.

For Rails >= 3.2

Simply put your mime types in config/initializers/mime_types.rb. send_file will take care of everything else.

For Rails < 3.2

Put your mime types in config/initializers/mime_types.rb. Additionally, tell send_file to use them (for ex...

After loading a staging dump into development, you might get an ActiveRecord::EnvironmentMismatchError when trying to replace the database (like rails db:drop, rails db:schema:load).

$ rails db:drop
rails aborted!
ActiveRecord::EnvironmentMismatchError: You are attempting to modify a database that was last run in `staging` environment.
You are running in `development` environment. If you are sure you want to continue, first set the environment using:

        bin/rails db:environment:set RAILS_ENV=development

Starting with R...

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, `...

You might have some trouble running a Rails LTS 2 app with MySQL 5.7.

If you don't want to hack Mysql 5.6 into your modern Ubuntu or use the MySQL sandbox, you might want to try MariaDB 10.x.

MariaDB 10.x should work with both old and new Rails applications.

[Switch to MariaDB](https://makandracards.com/makandra/468343-how-...

In Ruby on Rails, all the routes of a given application can be found within the config/routes.rb file.
You add more and more routes in this file as your project grows.

The problem here is that this file potentially becomes very complicated to manage over the time.
That’s why it’s important to find a way to order and maintain your routes.

See: Clean your Rails routes: grouping

Sometimes the routes.rb grows very fast and each line adds mo...

Using ActiveRecord's #signed_id and .find_signed methods you can create URLs that expire after some time. No conditionals or additional database columns required.

Instead of cobbling together default settings in several different places as the issues arise, you can define them application-wide.

Update RubyGems and Passenger

Bundler requires Rubygems >= 1.3.6. Run gem update --system if you have an older version.
It also is not compatible with older versions of passenger, so bring that up to date as well (2.2.15 works).

If you installed RubyGems through apt (which you should never do!), you may see a message giving you a hint to use apt to update.
Some people advise to install the 'rubygems-update-1.3.7' gem on Ubuntu systems if you used apt to install RubyGems.
I did that - and lost all...

The Rails logger will store its content in a buffer and write it into the file system every 1000 lines. This will come back to bite you when using Rails.logger.info to write log output during Rake tasks or on a production console.

You often won't notice this because for the development and test environments auto_flushing is set to write after each line. On production environments the Rails logger writes only every 1000 lines -- and not upon shell or script ter...

If a model inherits from others or uses many concerns / traits, it might be hard to see in the code which validators it has.
But fortunately there's a method for that:

irb(main):002:0> pp UserGroup.validators
[#<ActiveModel::Validations::InclusionValidator:0x00007f55efff97a8
  @attributes=[:deleted],
  @delimiter=[true, false],
  @options={:in=>[true, false], :allow_nil=>false}>,
 #<ActiveModel::Validations::InclusionValidator:0x00007f55f15748d0
  @attributes=[:cancelled],
  @delimiter=[true, false],
  @options={:in=>[true, false], ...

Let's say you have two screens:

1. Show a given project
2. Show a report for all projects

Ideally you want both screens to be handled by different controllers like this:

GET /projects/:id        => ProjectsController#show
GET /projects/report     => Projects::ReportsController#show

What seems like a simple requirement is a little awkward to configure in your routes.
Obviously the report should be a singleton resource, but how can we nest it into the Projects:: namespace?

What does not work is this:

resources :proj...

When you use google analytics to track your visitors interactions, you should ensure that it runs on your production site only. Otherwise it will spoil your statistics. To prevent this, test for the right environment and place the JS-code afterwards:

- if Rails.env.production?
  :javascript
    var _gaq = _gaq || [];
    _gaq.push(['_setAccount', 'UA-XXXXXXXX-X']);
    _gaq.push(['_trackPageview']);
    ...

See our new comprehensive guide for upgrading every Rails 2 version ever.

See our new comprehensive guide to upgrading every Rails 2 version ever.

If you get an error like this ...

 can’t find executable rails for rails-3.2.3 (Gem::Exception)

... one of several things might be wrong.

1. You're using RVM

It's possible that you have a system-wide gem executable (like rails) that requires a gem that is not available in the current RVM Ruby or gemset. Check what Ruby you are using (rvm current) and look out for .rvmrc files in your current directory (which change your Ruby upon entering the directory).

2. You killed a gem install process
   ----------...

The issue

Yesterday, Rails fixed a security issue (CVE-2014-3514) in Rails 4+. It was possible to use .where or .create_with to bypass Rails' Strong Parameters:

user.blog_posts.create_with(params[:blog_post]).create

would set all attributes on the blog post. After the fix, you have to properly whitelist the params, via `params[:blog_post].permit(:title, :bo...