validates_uniqueness_of is not sufficient to ensure the uniqueness of a value. The reason for this is that in production, multiple worker processes can cause race conditions:

1. Two concurrent requests try to create a user with the same name (and we want user names to be unique)
2. The requests are accepted on the server by two worker processes who will now process them in parallel
3. Both requests scan the users table and see that the name is available
4. Both requests pass validation and create a user with the seemingly available name...

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...

So you want to find out how many horizontal pixels you have available on a mobile device. This is super difficult because:

• Modern mobile devices have high-density displays where 1px in your CSS e.g. corresponds to 2.25, 4, ... physical pixels on the screen hardware.
• Difficult APIs
• Inconsistent APIs
• Screen orientation can change when the user rotates h...

With the impending release of Ruby on Rails 4, it looks like a lot of developers will be updating their web applications in the coming new year.

To help with this transition, over the next 31 days, we are going to be releasing a series of blog posts going over everything you will need to know about Rails 4 for an effortless upgrade.

Examples how to create dozens of shapes using pure CSS and a single HTML element.

You can define methods in any example group using Ruby's def keyword or define_method method. These helper methods are exposed to examples in the group in which they are defined and groups nested within that group, but not parent or sibling groups.

If you ever wondered why a constant wasn't defined or wasn't available where you expected it to be, this article will help.

Also see Ruby constant lookup: The good, the bad and the ugly.

jquery-timing is a very useful jquery plugin that helps to remove lots of nested anonymous functions. It's API provides you some methods that help you to write readable and understandable method chains. See yourself:

Example

// before
$('.some').show().children().doThat();
window.setTimeout(function(){
  $('some').children().doSomething().hide(function() {
    window.setTimeout(function() {
      otherStuffToDo();
    }, 1000);
  });
}, 500);

// after
$('.some').s...

As attachments to this card you will find a Cucumber feature and supplementing step definition that you can use to provoke Selenium focus issues that only occur when two focus-sensitive Selenium scenarios run at the same time (probably with parallel_tests). This can help you to detect and fix flickering integration tests.

The attached feature works by going to your root_path and focusing a random form element every 5...

This works in all relevant browsers:

document.activeElement

You can use this in your Selenium steps, for example, to assert that a form field is or is not focused.

When searching for text in a MySQL table, you have two choices:

• The LIKE operator
• FULLTEXT indexes (which currently only work on MyISAM tables, but will one day work on InnoDB tables. The workaround right now is to extract your search text to a separate MyISAM table, so your main table can remain InnoDB.)

I always wondered how those two methods would scale as the number of records incr...

Basic error pages

To add a few basic styles to the default error pages in Rails, just edit the default templates in public, e.g. public/404.html.

A limitation to these default templates is that they're just static files. You cannot use Haml, Rails helpers or your application layout here. If you need Rails to render your error pages, you need the approach below.

Advanced error pages

1. Register your own app as the applicatio...

If - for whatever reason - you have to render stylesheets dynamically, the following snippet might be of help. It emulates what "sprockets" would to when precompiling your assets, and give your stylesheets access to all the regular bells and whistles (like asset_path, proper @imports etc):

class DynamicStylesheetsController < ApplicationController

    def show
      logical_path = RELATIVE_PATH_TO_YOUR_TEMPLATE
      path = File.join(Rails.root, logical_path)
      template = Sass::Rails::SassTemplate.new(path)
      environment = ...

Git commits should be very deliberate, and only contain changes that you really want to be in there. In order to reduce the chance to accidentally commit something you didn't intend, review your changes before committing.

My preferred way of doing this is (only using git)

git add -N . # Add all paths, but not their contents
git add -p

Git will now show you all your changes in small chunks and ask you in an interactive mode whether you really want to add them.

The most helpful commands are

• y: yes (add the change)
• ...

Debugging .htaccess is hell, and RewriteRules in particular if they are not working as expected. But fear not! RewriteLog will help you out. \
Add this to your vhost's configuration:

RewriteLog "/tmp/rewrite.log"
RewriteLogLevel 9

After that, restart your Apache httpd and tail the above logfile.

When you are done and all is well: remember to remove those entries again, or set the log level to 0, to switch off rewrite logging.

You know that you can force absolute URLs throughout a response. Now you want to modify URLs similarly, but only in parts of a view (or controller) logic. Here is how.

Note: this has only been tested on a Rails 2 application. It should work similarly for Rails 3.

Put this into your ApplicationController:

def rewrite_options(*args)
  options = super
  options.merge!(:only_path => false) if @with_full_urls
  options
end...

As the title says: this jQuery plugin creates bar charts from HTML tables. It comes in some different flavors.

Check the examples page: http://alphagov.github.com/magna-charta/.

Rarely, you might want to rebuild all gems with native extensions, because they might be compiled against outdated system libraries, resulting in some warnings or even segfaults or other ruby errors.

You can do that using

gem pristine --all

This will reset all gems to a pristine state as if you'd reinstall them, and as a side effect, rebuild all native extensions.

The above command will also help you sorting out errors like this after a distribution upgrade:

libmysqlclient_r.so.16: cannot open shared object file: No such fil...

Icon fonts like Font Awesome are infinitely scalable, look great on high-DPI displays and will give your app a modern look.

However, icon fonts can be very awkward to use compared to raster icons. Elements are given icons by giving them a special class like icon-plus or icon-home:

<span class="icon-plus">Create</span>

The icon font's stylesheet will then recognize this class and insert the icon as the element's :before style.

In practic...

Under certain (unknown) circumstances, Rails will give localized files an invalid content-type in the Response header. For me, after requesting corporate_information and rendering corporate_information.de.html.haml, Rails sent a content-type of de.html instead of the expected text/html.

There are some discussions on this topic that offer workarounds, but no...