Question

While reading the Rails Guides, I came across something I’m unsure about. In the example, it shows that I can write a scope option that adds additional options towards checking uniqueness. My questions is, do I have to write out a method that queries specifically towards a time period. In other words, is there more code necessary than meets the eye in the example below? If not, how does Rails knows to check the right time stamp column in the table database?

class Holiday < ActiveRecord::Base
   validates :name, 
             :uniqueness => { :scope => :year,
             :message => "should happen once per year" }
end

Answer 1

All this does is ensure uniqueness in the context of a year column on your model – that column can be anything, but it needs to exist. It will not automagically check the year part of timestamp with a full date. Your model is responsible for actually storing the year value.

You can of course populate this year automatically. Let’s say you have a column holiday_date in your model. Then you can ensure that the year column is always set like so:

before_save :set_year

def set_year
  self.year = holiday_date.try(:year)
end

(The try methods just ensures that there’s no error if holiday_date happens to be nil)