Hashdown is a super lightweight rails plugin that adds hash-style lookups and option lists (for generating dropdowns) to ActiveRecord models. Note: Hashdown has been updated to support Rails 3. If you're looking for the original plugin version, it's in the rails 2 branch

Add this line to your application's Gemfile:

gem 'hashdown'

And then execute:

$ bundle

Or install it yourself as:

$ gem install hashdown

Given the following class definition:

class State < ActiveRecord::Base
  finder :abbreviation
end

You can look up states via their abbreviations like so:

@colorado = State[:CO]

By default, calling the finder method with a token that does not exist in the database will result in an ActiveRecord::RecordNotFound exception being thrown. This can be overridden by adding a :default option to your finder declaration.

class PurchaseOrder < ActiveRecord::Base
  finder :number, :default => nil
end

In this case, PurchaseOrder['00734'] will silently return nil if that number is not found.

These types of reference data models are often something you need to populate a select list on your form, so hashdown includes a method to generate your option list:

1. Declare your model to be selectable:

   class State < ActiveRecord::Base selectable end

2. Call select_options in your form to return a set of name, value pairs to pass into a select builder:

   <%= form.select :state_id, State.select_options %>

By default, selectable will return the :id of the record as the value, and the :name attribute value as the display. This can be overridden inline in the select_options call:

State.select_options(:name, :abbreviation)

The grouped_options_for_select format is also supported:

State.select_options(:group => :region)

Adding finder and selectable to a model is roughly equivalent to the following implementation:

class State < ActiveRecord::Base
  validates_uniqueness_of :abbreviation

  def self.[](state_code)
    where(abbreviation: state_code).first
  end

  def self.select_options
    all.map{|s| [s.name, s.id] }
  end
end

...except hashdown adds configuration for flexibility and caching for speedy lookups.

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request