When MySQL refuses to use your index, there's a number of things that you may be doing wrong. One of them might be conditions with improper data types.

An example

For example, let's assume you have a users table with an email field (varchar) which is indexed.

MySQL will use the index when your query is well-formed:

mysql> EXPLAIN SELECT * FROM users WHERE email = 'foo@example.com';
+----+-------------+-------+-------+----------------------+----------------------+---------+-------+------+-------+
| id | select_type |...

calc() lets you mix CSS units. Ever wanted to give an element "the container's width minus 20px on each side"? Here you go:

.foo {
  width: calc(100% - (20px * 2));
}

When using Sass, you need to interpolate Sass expressions:

$margin: 20px * 2

.foo
  width: calc(100% - #{$margin})

Supported by all modern browsers and IE9+.

tl;dr: Do not use merge! for session hashes. Use update instead.

Outline

Let's assume you're modifying the Rails session. For simplicity, let's also assume your session is empty when you start (same effect when there is data):

# In our example, we're in a Rack middleware
request = Rack::Request.new(env)
request.session.merge! :hello => 'Universe'
request.session
=> {}

Wat?

Even worse: When you inspect your request.session like above (e.g. in a debugger shell, o...

Safari & Chrome

Use $x() in your console:

$x('//span') # selects all span elements

Firefox

There's an add-on.

JavaScript has no built-in functions to compare two objects or arrays for equality of their contained values.

If your project uses Lodash or Underscore.js, you can use _.isEqual():

_.isEqual([1, 2], [2, 3]) // => false
_.isEqual([1, 2], [1, 2]) // => true

If your project already uses Unpoly you may also use up.util.isEqual() in the same way:

up.util.isEqual([1, 2], [2, 3]) // => false
up.util.isEqual([1, 2], [1, 2]) // => true

If you are wri...

MongoMapper is a MongoDB adapter for Ruby. We've forked it so it works for Rails 2.3.x applications running on Ruby 1.9. [1]

makandra/mongomapper is based on the "official" rails2 branch [2] which contains commits that were added after 0.8.6 was released. Tests are fully passing on our fork for Ruby 1.8.7, REE, and Ruby 1.9.3.

To use it, add this to your Gemfile:

gem 'mongo_mapper', :git => 'git://github.com/makandra/mongomapper.git', :branch => 'rails2'

...

If you open a pop-up window [1] in your Selenium tests and you want to close it, you can do this:

# Find our target window
handle = page.driver.find_window("My window title")

# Close it
page.driver.browser.switch_to.window(handle)
page.driver.browser.close

# Have the Selenium driver point to another window
last_handle = page.driver.browser.window_handles.last
page.driver.browser.switch_to.window(last_handle)

Mind these:

• find_window returns a window handle, which is something like `"{485fa8bd-fa99-...

Rails 2.3.16+ on Ruby 1.9 causes warnings like this:

.../gems/activesupport-2.3.17/lib/active_support/core_ext/string/output_safety.rb:22: warning: regexp match /.../n against to UTF-8 string

Many thanks to grosser for supplying a monkey-patch for Rails 2.3 (Commit f93e3f0ec3 fixed it for Rails 3). Just put it into config/initializers/ to make those warnings go away.

Since we're using RSpec on mos...

If you need to capture signatures on an IPad or similar device, you can use Thomas J Bradley's excellent Signature Pad plugin for jQuery.

To implement, just follow the steps on the Github page.

The form

If you have a model Signature with name: string, signature: text, you can use it with regular rails form like this:

- form_for @signature, :html => { :class => 'signature_form' } do |form|
  %dl
    %dt
      = form...

If others on a call (Skype, SIP, ...) can not hear you loud enough, your volume levels are probably too low. Also, Skype may be changing your mixer levels.

Set a proper recording volume

1. Open your mixer software (run pavucontrol).
2. Switch to input devices.
3. If you have more than one recording device, find the correct one.
4. Make a test call to a colleague that can tell you if it's too loud or too quiet.
5. Drag the volume slider for your input device to an adequate level -- for me, 75% (-7.46dB) work fine. 100% is usually way to...

You either have an old version of Mocha and an edge version of Rails 3.2, or you have a new version of Mocha and an old version of Rails. The best solution is to update Mocha to the latest version and switch to Rails edge.

If you are using shoulda-matchers or another gem that locks Mocha to an old version, you are out of luck.
More info with many other workarounds that you do not want to use can be found here. A hack to work around this case is to add the following file to lib/mocha/setup.rb:...

This page lists many query methods and options in ActiveRecord which do not sanitize raw SQL arguments and are not intended to be called with unsafe user input. Careless use of these methods can open up code to SQL Injection exploits. The examples here do not include SQL injection from known CVEs and are not vulnerabilites themselves, only potential misuses of the methods.

Please use this list as a guide of what not to do.

Stringex is a gem that offers some extensions to Ruby's String class. Ruby 1.9 compatible, and knows its way around unicode and fancy characters.

Examples for stringex's String#to_url method:

# A simple prelude
"simple English".to_url => "simple-english"
"it's nothing at all".to_url => "its-nothing-at-all"
"rock & roll".to_url => "rock-and-roll"

# Let's show off
"$12 worth of Ruby power".to_url => "12-dollars-worth-of-ruby-power"
"10% off if you act now".to_url => "10-percent-off-if-you-act-now"

# You do...

You probably know that you can use CSS selectors to match against elements and their attributes, such as:

a[title] { /* any <a> that has a "title" */ }
a[data-fancy="true"] { /* any <a> that has their "data-fancy" attribute set to "true" */ }

But there is more: You do not need to match against "full" attribute values but can match against parts of them.

They work in all somewhat modern browsers, and IE9 or later.

Match variants

Exact match (CSS2)

[foo="bar"] (matches `<div foo="b...

You can use the content CSS attribute to set an element's content -- which is especially useful for the :before and :after pseudo elements:

a:before {
  content: 'Click me: ';
}

The above example would prepend "Click me:" to any link on the page.

Note that you can also refer the contents of other attributes of the element. So, if your links have a helpful title set, you could do this:

a:before {
  content: attr(title) ": ";
}

There also is a jsFiddle for the examp...

Ruby has two different ways to match the start and the end of a text:

• ^ (Start of line) and $ (End of line)
• \A (Start of string) and \z (End of string)

Most often you want to use \A and \z.

Here is a short example in which we want to validate the content type of a file attachment. Normally we would not expect content_type_1 to be a valid content type with the used regular expression image\/(jpeg|png). But as ^ and $ will match lines, it matches both content_type_1 and content_type_2. Using \A and \z will wo...

Virtualization

Microsoft provides virtual machines for different Internet Explorer versions.

The images are available for various virtualization solutions, including VirtualBox.

BrowserStack

For a monthly fee browserstack.com provides access to various versions of Windows and Internet Explorer through your web browser. It's pretty convenient.

By installing a Chrome addon you can ...

Spreewald now comes with a step that tests if a form field is visible:

Then the "Due date" field should be visible
But the "Author" field should not be visible

The step works by looking up the field for the given label, then checks if that field is hidden via CSS (or Javascript).

It is not currently tested if the label is visible or hidden. For this see: [Check that an element is visible or hidden via CSS with Cucumber/Capybara](https://makandracards.com/makandra/1049-check-that-an-elem...

Consul 0.6.1+ gives your Power class a number of static methods that behave neutrally in case Power.current is nil. This allows you to create authorization-aware models that still work when there is no user at the end of a web browser, e.g. on the console, during tests or during batch processes.

You will often want to access Power.current from another model, to e.g. iterate through the list of accessible users:

class UserReport

  def data
    Power.current.users.c...

We recently had a problem on a Memcache cluster, where one of the servers showed a significantly worse cache hit rate and a lot more evictions.

It turned out that the only reason was that the server was running for a few months longer than the others. Some investigation showed this to be a known problem with Memcache: Once your cache gets full, it might be "hardwired" for your specific usage patterns. If those change (and you for example start to store larger values), memory is no longer allocated optimally, in extreme cases Memcache might ...

The problem

Calling bundle update GEMNAME will update a lot more gems than you think. E.g. when you do this:

bundle update cucumber-rails

... you might think this will only update cucumber-rails. But it actually updates cucumber-rails and all of its dependencies. This will explode in your face when one of these dependencies release a new version with breaking API changes. Which is all the time.

In the example above updating cucumber-rails will give you Capybara 2.0 (because capybara is a dependency of `cucumber-rail...

Calling bundle update (without arguments) updates all your gems at once. Given that many gems don't care about stable APIs, this might break your application in a million ways.

To stay sane, update your gems using the applicable way below:

Projects in active development

Update the entire bundle regularily (e.g. once a week). This ensures that your libraries are up-to-date while it's easy to spot major version bumps which may break the app.

Projects that have not been updated in a while

1. [Update a single gem conservatively](htt...

If you get a message like this:

Jan 21 13:42:38 foobar syslogd: /var/log/authlog : no such file or directory

But you are sure the file exists and it have the correct permissions:

# example for Solaris 9
-rw-r--r-- 1 root sys 8,0K 21. Jan 13:51 /var/log/authlog

Then you perhaps have a trailing whitespace after /var/log/authlog in the /etc/syslog.conf.

Note: Use TAB to separate log components from log file names in Solaris. Because spaces do not work.