Rake task for writing YAML-formatted test fixtures using current database

db_fixtures.rake

namespace :db do
  namespace :fixtures do
    desc "Write YAML-formatted test fixtures using current database"
    task :write_yml, [:limit] => [:environment] do |t, args|
      args.with_defaults(:limit => nil)
      write_active_record_tables('.yml', args.limit) do |output_stream, records|
        # Important not to write the records as an array; write them as a hash.
        # Use the "id" as the unique hash key. This formats the fixture in
        # standard unordered layout.
        hash = {}
        records.each { |record| hash["#{record.class.table_name.singularize}_#{record.id}"] = record.attributes }
        output_stream.write(hash.to_yaml)
      end
    end

    # Answers an array of table-name strings, one string element for every
    # database table with a matching model under app/models. Table names are
    # plural, as standard. Assumes that you have already established the
    # active-record connection.
    def active_record_tables
      ActiveRecord::Base.connection.tables.select do |table_name|
        File.exists?(File.join(Rails.root, 'app', 'models', table_name.singularize + '.rb'))
      end
    end

    # Iterates through every table, opening an appropriate fixture file at
    # spec/fixtures. Then invokes the given block, passing the output stream and
    # array of active records. Your block writes the records using a format
    # matching the given extension, i.e. YAML or CSV.
    def write_active_record_tables(extension, limit)
      active_record_tables.each do |table_name|
        klass = table_name.classify.constantize
        records = klass.limit(limit).all
        puts "Writing #{records.length} #{klass} fixtures"
        yield File.open(File.join(Rails.root, 'spec', 'fixtures', table_name + extension), 'w'), records
      end
    end
  end
end