url validation in ruby on rails

1)Url field should also accept url as “www.abc.com”. If user enters url like this, it should be automatically appended with “http://” resulting in 开发者_JAVA技巧value saved in database as “http://www.abc.com”. If user enters url as “http://www.xyz.com” system should not append “http://”. User should be able to save url with “https://”. what is the code for it in ruby on rails?

This code worked:

def validate
  if !self.external_url.blank? && self.external_url != "external url"
    if self.external_url.match(/^(http|https):\/\/[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,5}(([0-9]{1,5})?\/.*)?$/ix).nil?
      if self.external_url.match(/^[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,5}(([0-9]{1,5})?\/.*)?$/ix).nil?
        self.errors.add :base, 'External url is invalid' #message is changed by Hemant
      else
        self.external_url = "http://"+self.external_url
      end
    end
  end
end

Not a great way to ask for assistance which is why I suspect you've been down voted twice!

I would suggest you start by looking at before_validation, validates_format_of and regular expressions. See how you get on with those and perhaps post any updates if you get stuck.

Ps:

prepend = "To attach to the beginning of data" append = "To attach to the end of the data"