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Simple, dynamic and efficient activerecord model constants.
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Simple, dynamic and efficient activerecord model constants.

Ever wanted to be able to be able to do something like:

case buoy.buoy_type
when BuoyType::NOAA
when BuoyType::SCRIPPS


Bouy.create(:name => :foo, :bouy_type => BuoyType::NOAA)

but weren't sure the best / most efficient way to implement?

One way would be to do something like:

class BuoyType < ActiveRecord::Base
  NOAA = find_by_name('noaa')

However, this approach can become tedious and tough to manage.

Another way would be to dynamically create the constants for all the rows in the given table at rails start. However, for models w/hundreds of rows, e.g., Country, City, this wouldn't be very efficient either.

This gem minimizes the db calls by memoizing the finder that is used to look up the constant values. So, it depends on your app server but only the first refernece to a given constant should require a db query (see the code and specs for more details).


Manual Install

Standard gem install:

gem install constantize

After installing the gem you would need to require it:

require 'constantize'

Rails 2.x / No Bundler

In a Rails 2.x project you can add this to your environment.rb:

config.gem 'constantize'

followed by:

rake gems:install

Rails 3.x / Bundler

In Rails 3.x add this to your Gemfile:

gem 'constantize'

followed by:

bundle install


In the model that you will be "constantizing" simply add the following to the top:

constantize :key

where :key is the name of the field that will be used to build the finder.


class BuoyType < ActiveRecord::Base
  constantize :name

this would assume that your buoy_types table looked something like:

| id | name    |
|  1 | noaa    |
|    ..        |

if your table used a different field, say :title, rather than :name:

| id | title   |
|  1 | noaa    |
|    ..        |

then your model definition would look like:

class BuoyType < ActiveRecord::Base
  constantize :title

Finally, if you wanted only the :id to be returned from the constant call (rather than the entire model) you could do:

class BuoyType < ActiveRecord::Base
  constantize :name, :id

and your call to BuoyType::NOAA would return only the interger :id value (1 in this case).

Note on Patches/Pull Requests

  • Fork the project.
  • Make your feature addition or bug fix.
  • Add tests for it. This is important so I don't break it in a future version unintentionally.
  • Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
  • Send me a pull request. Bonus points for topic branches.


Copyright (c) 2010 Adam Weller. See LICENSE for details.

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