When doing a presentation you may want to hide your desktop icons.

You can switch them off (or back on) like this:

• Open up gconf-editor
• Navigate to apps -> nautilus -> preferences
• (Un)check "show_desktop"

After switching to Rails 3 you may get a LoadError with the following message when trying to use your application via passenger:
no such file to load -- dispatcher

Your Passenger version is most likely out of date.

Update the gem, then install the apache module again:
sudo gem install passenger
sudo passenger-install-apache2-module

Follow any instructions. Update your /etc/apache2/httpd.conf with the lines given at the end of the installation process to use the version you just installed.

You might find that your Passenger ignores all RailsSomething directives in the vhost for your new Rails 3 application. The culprit is a file config.ru which makes Passenger consider your application a Rack (non-Rails) application.

To fix this you can either use RackEnv in lieu of RailsEnv (it works fine) or delete the config.ru. Unless you have a good reason to do so, go with RackEnv.

You will need to upgrade to RSpec >= 2 and rspec-rails >= 2 for Rails 3. Here are some hints to get started:

• In RSpec 2 the executable is rspec, not spec.
• RSpec and rspec-rails have been completely refactored internally. All RSpec classes have been renamed from Spec::Something to RSpec::Something. This also means that every require 'spec/something' must now be require 'rspec/something'.
• In spec_helper.rb, Spec::Runner.configure becomes RSpec.configure
• It has become really hard to extend specific example groups ...

Be careful when using params.merge as params is a HashWithIndifferentAccess.

Why?

Usually this should not be an issue but it turns crazy if you try to include associated models deeper than 1 level:
options = params.merge(:include => { :user => :avatar })
Post.paginate options

When inspecting the merged params you will get something like this:
{ :include=> { "user" => :avatar }, :page => 23 }

Here the :user symbol in the hash of inclusions turned into a "user"...

In rare cases you might need something like form_for (for using form builder methods on the resulting block element) but without the surrounding form. One such case would be updating some of a form's fields via XHR.

You can simply use Rails' fields_for to do things like this in your views (HAML here):

- fields_for @user do |form|
  = form.label :email, 'E-Mail'
  = form.text_field :email

You will only receive the form content you gave, no hidden inputs incl...

I prefer the application that I'm currently working on to be reachable at http://localhost/.

So when I switch to another project, I use this handy shell script to set one site as the current one. Call it just like this:
apache-site makandra-com

Note that it disables all other sites in your Apache configuration so you would not want to use this on production machines.
Furthermore it will also enable the default site if that was available.

When you call apache-site with no arguments, it will list all available sites.

...

When using form_for you can give the form's target URL either as a string or an array:

form_for(admin_user_path(@user)) do ... end
# same as:
form_for([:admin, @user]) do ... end

Same for link_to:

link_to("Label", edit_admin_user_path(@user))
# same as
link_to("Label", [:edit, :admin, @user])

polymorphic_path and polymorphic_url

If you would like to generate a path or URL string from an array of route components just as form_for does, you can use polymorphic_path or polymorphic_url:

polymorphic...

If you previously used version 2.x of Thunderbird and upgraded to 3.x (for example through an Ubuntu release upgrade) you might notice that Thunderbird will not show any of your old e-mails or settings.

This results from a different directory being used for storing profiles and configuration.

You can replace the blank profile with your old one like this:
cd ~
mv .thunderbird .thunderbird-invalid
cp -R .mozilla-thunderbird .thunderbird

Upon its next start, Thunderbird brings up the migration wizard introducing you to a few vers...

If you need to look at the list of methods that are called upon certain events (like before/after saving etc), do this:

Model._save_callbacks.select {|cb| cb.kind == :before}.map{ |c| c.instance_variable_get :@filter }

Rails 2

User.after_save_callback_chain

To look at the method names only, you could do something like that:

User.after_save_callback_chain.collect(&:method)

This can be helpful when you need the latest file inside a directory for processing in a shell script:

ls -1tr * | tail -1

Used switches

The -1 switch makes ls return 1 file per line, -t orders by modification time and -r causes sorting from oldest to newest. tail -1 then returns the last line, containing the newest file's name.

If you require only a subset of files, adjust the "*" mask accordingly or use other switches of ls.

If you did file operations inside a shell or for example using Nautilus, it can take quite a while until RubyMine takes note of them and updates things like your project tree or its internal file list.

Flushing file system buffers helps you out (run it from a terminal):
sync

This is also possibly via the RubyMine menus: File → Synchronize.

Take care when trying to set attributes to nil in a blueprint.

Given the following master blueprint:
Story.blueprint do
title
author { User.make }
editor { User.make }
end

This approach will not overwrite/remove the editor defined in the master blueprint:
Story.blueprint(:draft) do
editor nil
end

...whereas this one will (note the lambda):
Story.blueprint(:draft) do
editor { nil }
end

If you get an ActiveRecord::RecordNotSaved error, a method inside one of your model's callback chains (before_save etc) possibly returned false.

This commonly happens when you have a method setting attributes and the last one is a boolean set to false (as the value of the last statement is returned). Fix this by simply calling true at the end of such methods:

def hide
  self.visible = false
  true
end

Note that nil won't cause this behavior. Thus, you can use an if without problems -- if you are not returning fal...

Sometimes the order in which strings appear on a page matters to you.

Spreewald gives you steps like these:

Then I should see in this order:
  | Alpha Group |
  | Augsburg    |
  | Berlin      |
  | Beta Group  |

Or, if you prefer multiline strings:

Then I should see in this order:
  """
  Alpha Group
  Augsburg
  Berlin
  Beta Group
  """

The step ignores all HTML tags and only tests on plain text.

When you do tags with acts-as-taggable-on and want to preload associated tags, you can do so with

TaggedModel.scoped(:include => :tag)

Note however that this will only prevent tagged_model.tags from hitting the database. Using tagged_model.tag_list does not use the preloaded association.

Did you use the :select option in a find, and forgot to include foo?