Rails3 で URLが『hoge.com/〜』の時に『www.hoge.com/〜』にリダイレクトする場合のメモ

(Rails3.2.12)

config/routes.rb

• Redirect www Subdomain to Your Apex Domain Using the Rails Router | Big Nerd Ranch
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  constraints(host: /^(?!www\.)/i) do
    match '(*any)' => redirect { |params, request|
      URI.parse(request.url).tap { |uri| uri.host = "www.#{uri.host}" }.to_s
    }
  end