How do I use a YAML file instead of seeds.rb to load the initial data into a database?
Check out the Ruby on Rails Guide to fixtures:
http://guides.rubyonrails.org/testing.html#the-low-down-on-fixtures
Generally, you can create YAML fixture files in the test/ directory and then load them into your database using the rake db:fixtures:load command. The full documentation on all the cool things you can do with fixtures is here:
http://api.rubyonrails.org/classes/Fixtures.html