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Learning Rails: Live Edition by Edd Dumbill, Simon St. Laurent

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A Place on the Calendar

You could test date components individually, but more typically you’ll want to test whether or not the date falls within a given range. Rails makes this easy with the validates_inclusion_of method, already examined previously, and its inverse, validates_exclusion_of:

# Restrict birthday to reasonable values, i.e., not in the future and not
# before 1900
validates_inclusion_of :birthday,
  :in => Date.civil(1900, 1, 1) .. Date.today,
  :message => "must be between January 1st, 1900 and today"

The :in parameter actually takes a list of possible values (an enumerable object, technically), and in this case the definition creates a list of values between January 1, 1900 (thanks to the Date.civil method) and today’s date (thanks to the Date.today method).

Testing for Presence

The :allow_nil parameter noted earlier lets you say that things don’t need to be present, but there are also times when the only validation you want to perform is to make certain that a given field contains a value. In this case, validates_presence_of is extremely convenient:

# Finally, we just say that favorite time is mandatory. 
# While the view only allows you to post valid times, remember 
# that models can be created in other ways, such as from code
# or web service calls. So it's not safe to make assumptions
# based on the form.
validates_presence_of :favorite_time

As the comment reminds, while an HTML form can make some explicit demands of users, you should avoid writing code that assumes that ...

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