foo.rb

# in seeds/foo.rb
class Seeds
  class Foo
    def self.call
      ::Foo.create! NAMES.map{|n| { name: n } }
    end
  end
end

seeds.rb

class Seeds
  NAMES = %w[foo bar wee].freeze

  def self.call
    Dir[Rails.root.join 'db/seeds/*.rb'].sort.each do |seed|
      require seed
      cls = "Seeds::#{File.basename(seed, '.rb').classify}".constantize
      cls.()
    end
  end
end

Seed.()