In Rails 2.3.4 there’s a new rake task called db:seed that allows you to seed your database with data. To use it you first need a file called db/seed.rb. In it put the code that creates the ActiveRecord objects your application needs.

You can load and execute SQL from an external file, or plain Ruby objects from YAML or JSON as I’ll show you in this example.

Put this in db/seed.rb:

   1  json = ActiveSupport::JSON.decode(File.read('db/seeds/countries.json'))
   2  
   3  json.each do |a|
   4    Country.create!(a['country'])
   5  end

Next export the data from an existing database by running the following command in the Rails console:

   1  File.open('db/seeds/countries.json', 'w') { |f| f << Country.all.to_json }

Now when you run rake db:seed, Rails will load the countries.json file and insert the data into your database.

Pretty print JSON data

You’ll probably want to pretty print your data if you’re going to manually edit it. This can be done by following the instructions in this snippet

In lib/tasks/app.rake:

   1  namespace :db do
   2    desc "Bootstraps the database"
   3    task :bootstrap => ['db:schema:load'] do
   4  
   5     { 'Ruby' => 'ruby',
   6        'JavaScript' => 'javascript',
   7      }.each do |name, short_name|
   8        Category.create!(:name => name, :short_name => short_name)
   9      end
  10  
  11    end
  12  end