Question

I have a simple model

class Task < ActiveRecord::Base
  validates :deadline, :if => :deadline_in_future?

  def deadline_in_future?
    Date.today < self.deadline
  end
end

All seems ok, but when I in my rails console

irb(main):001:0> Task.new
ArgumentError: You need to supply at least one validation

Where is the problem?

Answer 1

You forgot to tell validates how you want to validate :deadline. I think you’re misunderstanding what :if does; the :if => :deadline_in_future? option means:

Validate :deadline only if the deadline_in_future? method returns a true value.

I suspect that you want to validate that the deadline is in the future:

validate :deadline_in_future?

Further details are available in the Active Record Validations and Callbacks Guide.