Question

Using Ruby/RoR – The year is a string in the model/view. How do I validate that the user entered string is a valid gregorian calendar year?

Answer 1

At the cost of a tiny bit of cleverness/regexp magic, something like the following will allow you to test not only for whether a string is numeric (the first criteria for being a valid year) but for whether it falls within a particular range of years:

def is_valid_year?(date_str, start=1900, end=2099)
  date_str.grep(/^(\d)+$/) {|date_str| (start..end).include?(date_str.to_i) }.first
end

The above function returns nil for any string with non-numeric characters, false for those which are numeric but outside the provided range, and true for valid year strings.