How to validate that a string is a year

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

It sounds like a more direct question is: how do you validate that the user enters a string corresponding to a number between 1582 and 2500 (say). You can do this like this:

 date_string.scan(/\D/).empty? and (1582..2500).include?(date_string.to_i)

that way, you can choose what a sensible year is, too - for example, is 800 really a valid answer in your application? or 3000?

Answer 2

Here's one way to do it:

Date.strptime(date_str, "%Y").gregorian?

Note that this will throw exceptions if the string is in an unexpected format. Another (more forgiving) option, is:

Date.new(date_str.to_i).gregorian?

Answer 3

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.

Answer 4

The accepted answer by @rcoder will not be working as i tested on rails 4+ . i made another simple one.

def is_valid_year? year
  return false if year.to_i.to_s != year
  year.strip.to_i.between?(1800, 2999)
end

The first line to not accept characters, you can also change the range between as you wish

Answer 5

Date.parse(string_of_date).gregorian?

Also, have a look at the documentation for the Date class.

Answer 6

Wanting to parse an integer from a string is a pretty common question for Ruby. Probably because there's no perfect approach. Maybe it deserves its own tag!

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