Hi Sirs,

Many tutorials over the web shows how to load data from fixtures. But, if you want to migrate your mysql data to a postgresql database?

We can export our data to fixtures, and after that we can load the fixtures to every database management system we wish.

Let's go to the rake task:

desc "export the database models to YML fixtures" 
task(:models_to_fixtures => :environment) do 
  ActiveRecord::Base.establish_connection(
    :adapter => 'postgresql', # mysql, sqlite3
    :encoding => 'utf8',
    :database => 'cnxs_development',
    :username => 'username',
    :password => 'secret'
  )
  ActiveRecord::Base.connection

  if ENV['MODELS'].nil? || ENV['MODELS'].blank?
    raise "Please enter valid models names separated by coma. Ex: MODELS=User,Account"
  end

  models = ENV['MODELS'].split(',').collect { |arg| arg.camelize.constantize }

  models.each do |model|
    output = {}
    collection = model.find(:all)
    collection.each do |object|
      output.store(object.to_param, object.attributes)
    end
    file_path = "#{RAILS_ROOT}/tmp/#{model.table_name}.yml" # /tmp/
    File.open(file_path, "w+") { |file| file.write(output.to_yaml) }
  end
end

Here you need to fill your database attributes like you do in the /config/database.yml.

You will call the command line:

$ rake models_to_fixtures MODELS=<your model names separated by coma>

For example:

$ rake models_to_fixtures MODELS=User,Post

All your model data will be stored on /tmp/ directory.

Download this rake task here.

See you.