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"...

Need form builder helpers without emitting a surrounding <form> tag, for partial updates such as XHR-driven field changes. Rails fields_for yields the same builder without hidden inputs or authenticity token.

Quickly make one Apache virtual host available at localhost while switching projects. The script disables other sites, can re-enable the default site, and lists available sites without arguments.

polymorphic_path and polymorphic_url build route strings from arrays of model objects or route components, including :new and :edit prefixes. Nested Active Record namespacing can fail to resolve the correct route.

The timepicker addon adds a timepicker to jQuery UI Datepicker, thus the datepicker (jQueryUI) is required for using any of these. In addition all datepicker options are still available through the timepicker addon.

I’m going to list assumptions your systems probably make about names. All of these assumptions are wrong. Try to make less of them next time you write a system which touches names.

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...

The ancestry gem allows you to easily use tree structures in your Rails application.

There is one somewhat unobvious pitfall to it: its way of applying the orphan_strategy which defines how it handles children of an object going to be destroyed.

What's this all about?

In many cases you might want to disallow destruction if there are any child nodes present. The restrict strategy does the trick but raises an exception when destroy is called:
has_ancestry :orphan_st...

Rails models expose callback chains for save events, making it possible to inspect registered before and after methods and identify method names.

Get the most recently modified file in a directory for shell script processing using ls -1tr and tail -1.

RubyMine may lag behind file operations done outside the IDE, leaving the project tree and file list stale. sync or File → Synchronize forces an update.

Blueprint attributes in Machinist can keep inherited values unless nil is wrapped in a block; editor { nil } clears the master value, plain nil does not.

ActiveRecord::RecordNotSaved often comes from a callback method returning false, especially when the last assignment is boolean. Ending the method with true avoids the save being aborted.

Lately, we’ve been exploring ways to offer web apps that perform like native apps on mobile devices. For this short sprint we targeted mobile WebKit browsers—especially the default browsers on iOS and Android—because of their widespread use and excellent support for HTML5 and CSS3. Here are a few things we’ve learned along the way.

Verify that page text appears in a specific sequence while ignoring HTML markup, using a Cucumber step for plain-text order checks.

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.

ActiveRecord::MissingAttributeError appears when a query omits a column later accessed on the model, often after using select with too few fields.

SSL in Rails 3 is non-obvious.

Named Machinist blueprints can reuse another blueprint’s fields, letting variants combine shared defaults without repeating attribute definitions.

Array(...) is a convenient coercion in Ruby, but to_a can split strings and trigger unexpected conversions for non-array inputs.

Private Paperclip downloads need restricted storage or hashed URLs to keep attachments away from public access. A controller-based delivery path or secret-based paths reduce exposure.

You need to install the following packages before you can build the Nokogiri gem:

sudo apt-get install libxml2-dev libxslt1-dev

If you get an error message like that you are missing the Aspell files a specific language:

No word lists can be found for the language "de"

Solve it by installing the proper package, e.g. on Ubuntu:

sudo apt-get install aspell-de