ensure uri fields have a valid protocol. HTTP by default

uri_field.rb

module Concerns::URIField
  extend ActiveSupport::Concern

  included do 
    def self.ensure_valid_protocol_in_uri(field, default_protocol = "http", protocols_matcher="https?")
      define_method "#{field}=" do |new_uri|
        if new_uri.present? and not new_uri =~ /^#{protocols_matcher}:\/\//
          new_uri = "#{default_protocol}://#{new_uri}"
        end
        super(new_uri)
      end
    end
  end
end

# Usage in models:
# include Concerns::URIField
# ensure_valid_protocol_in_uri :some_link