How do I validate restful parameters in rails at the routing level?

I currently have the following re开发者_Go百科stful url:

/questions/2011/05/

My route for questions is:

match 'questions/:year/:month/' => 'Questions#month'

How can I validate the above year and month parameters at the route level so that:

1. year and month are integers
2. min/max length of year = 4
3. min/max length of month = 2

In django, I can do the above with the following line:

url(r'^questions/(?P<year>\d{4})/(?P<month>\d{2})/$', 'questions.views.month'),

I'm looking through the rails guide and googling around and I cannot find the corresponding functionality at the routing level. Is the above meant to be done at the controller level?

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You are looking for the constraints option to the match method options hash.

match 'questions/:year/:month/' => 'questions#month', :constraints => {:year => /\d{4}/, :month => /\d{2}/}

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