rails can't find database.yml - ruby-on-rails

Question

I just removed my database.yml because I'm trying to use Mongoid, and now I'm getting the following:
$ rails server
=> Booting WEBrick
=> Rails 3.0.9 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
Exiting
/usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/application/configuration.rb:88:in `read': No such file or directory - /home/chris-kun/code/thirsty/config/database.yml (Errno::ENOENT)
from /usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/application/configuration.rb:88:in `database_configuration'
from /usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.9/lib/active_record/railtie.rb:58:in `block (2 levels) in <class:Railtie>'
from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.0.9/lib/active_support/lazy_load_hooks.rb:36:in `instance_eval'
from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.0.9/lib/active_support/lazy_load_hooks.rb:36:in `execute_hook'
from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.0.9/lib/active_support/lazy_load_hooks.rb:26:in `on_load'
from /usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.9/lib/active_record/railtie.rb:57:in `block in <class:Railtie>'
from /usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/initializable.rb:25:in `instance_exec'
from /usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/initializable.rb:25:in `run'
from /usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/initializable.rb:50:in `block in run_initializers'
from /usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/initializable.rb:49:in `each'
from /usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/initializable.rb:49:in `run_initializers'
from /usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/application.rb:134:in `initialize!'
from /usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/application.rb:77:in `method_missing'
from /home/chris-kun/code/thirsty/config/environment.rb:5:in `<top (required)>'
from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.0.9/lib/active_support/dependencies.rb:239:in `require'
from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.0.9/lib/active_support/dependencies.rb:239:in `block in require'
from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.0.9/lib/active_support/dependencies.rb:225:in `block in load_dependency'
from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.0.9/lib/active_support/dependencies.rb:596:in `new_constants_in'
from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.0.9/lib/active_support/dependencies.rb:225:in `load_dependency'
from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.0.9/lib/active_support/dependencies.rb:239:in `require'
from /home/chris-kun/code/thirsty/config.ru:3:in `block in <main>'
from /usr/lib/ruby/gems/1.9.1/gems/rack-1.2.3/lib/rack/builder.rb:46:in `instance_eval'
from /usr/lib/ruby/gems/1.9.1/gems/rack-1.2.3/lib/rack/builder.rb:46:in `initialize'
from /home/chris-kun/code/thirsty/config.ru:1:in `new'
from /home/chris-kun/code/thirsty/config.ru:1:in `<main>'
from /usr/lib/ruby/gems/1.9.1/gems/rack-1.2.3/lib/rack/builder.rb:35:in `eval'
from /usr/lib/ruby/gems/1.9.1/gems/rack-1.2.3/lib/rack/builder.rb:35:in `parse_file'
from /usr/lib/ruby/gems/1.9.1/gems/rack-1.2.3/lib/rack/server.rb:162:in `app'
from /usr/lib/ruby/gems/1.9.1/gems/rack-1.2.3/lib/rack/server.rb:253:in `wrapped_app'
1 #!/usr/bin/env ruby
from /usr/lib/ruby/gems/1.9.1/gems/rack-1.2.3/lib/rack/server.rb:204:in `start'
from /usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/commands/server.rb:65:in `start'
from /usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/commands.rb:30:in `block in <top (required)>'
from /usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/commands.rb:27:in `tap'
from /usr/lib/ruby/gems/1.9.1/gems/railties-3.0.9/lib/rails/commands.rb:27:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'
Any ideas?

Answer 1

In config/application.rb, remove the line require 'rails/all' and replace with:
require "rails"
%w(
action_controller
action_mailer
active_resource
rails/test_unit
).each do |framework|
begin
require "#{framework}/railtie"
rescue LoadError
end
end
(This is the contents of rails/all.rb in the railties gem, but with the activerecord line removed).

Answer 2

I had a similair issue before, but it turns out I had some scattered active_record references lying around. Full credit to Dylan Markow for this one!
Removing database.yml when using Mongoid in Rails 3.2
Execute grep -r active_record config/ to find all references, then comment them out!

Answer 3

For those of you who want to use db related functions ex) rake db:seed with mongoid, also add the mongoid railtie:
https://github.com/mongodb/mongoid/tree/master/lib/mongoid/railties
require "rails"
# Import gems in Gemfile
Bundler.require(*Rails.groups)
# important that this is imported after gems in Gemfile are imported
%w(
mongoid
action_controller
action_mailer
active_resource
rails/test_unit
).each do |framework|
begin
require "#{framework}/railtie"
rescue LoadError
end
end

Answer 4

An updated answer for Rails 5 and all future versions of Rails:
You should be using the require snippet from the rails/all.rb file that is current with your version of Rails without the active_record railtie. Here is a link to rails/all.rb on the Rails master branch.
As of writing this it includes a number of new railties which you don't want to miss out on:
require "rails"
%w(
action_controller/railtie
action_view/railtie
action_mailer/railtie
active_job/railtie
action_cable/engine
rails/test_unit/railtie
sprockets/railtie
).each do |railtie|
begin
require railtie
rescue LoadError
end
end