Rails Validating on a virtual attribute, setting form error. Railscast #32

I'm basically attempting to implement the solution from Railscast #32, modernized for Rails 3.0.7

http://railscasts.com/episodes/32-time-in-text-field

class Task < ActiveRecord::Base

attr_accessible :description, :complete, :deadline

validate :deadline_string_no_errors


def deadline_string
  self.deadline.to_s
end

def deadline_string=(deadline_str)
  unless deadline_str.blank?
    begin
      self.deadline = Chronic.parse(deadline_str)
    rescue
      self.deadline = Time.parse(deadline_str)
    rescue
      @deadline_invalid = true
    end
  end
end

def deadline_string_no_errors
  errors.add(:deadline_string, "Is Invalid") if @deadline_invalid
end

I want to set a validation error when a string, such as 'fooba开发者_如何学Gor' is put into #deadline_string=, either by console or (intended) form entry.

What I'm particularly concerned about is a more strict formatting of time, Chronic.parse('2011-05-25 08:19:00 UTC') Which throws a TypeError. In that case I want to fallback to Time.parse, which can understand this formatting.

This alternative form also does not work with deadline_string="foobar" as the initial call.

# snip
def deadline_string=(deadline_str)
  unless deadline_str.blank?
    self.deadline = ( parse_time(deadline_str, Chronic) || parse_time(deadline_str, Time) )
  end
end

private

def parse_time(string, parser)
  begin
    parser.parse(string)
  rescue
    @deadline_invalid = true
  end
end

def deadline_string_no_errors
  #snip
end

No matter what I try it doesn't ever seem to get to the second rescue. There is also some strangeness around the deadline attribute, which is specified in the schema as a datetime.

The solution in the end was something like this, but it could probably stand to some refactoring. I'm anxious about setting self.deadline in the method call, but not sure why I should be.

Class Task < ActiveRecord::Base
  attr_accessible: description, :complete, :deadline

  validate :deadline_string_no_errors

  def deadline_string
    self.deadline.to_s
  end

  def deadline_string=(deadline_str)
    unless deadline_str.blank?
      self.deadline = ( parse_time(deadline_str, Chronic) || parse_time(deadline_str, Time) )
      @deadline_invalid = true if self.deadline.nil?
    end
  end

  private

  def parse_time(string, parser)
    begin
      parser.parse(string)
    rescue
    end
  end

  def deadline_string_no_errors
    errors.add(:deadline_string, "Is Invalid") if @deadline_invalid
  end

Refactoring is welcome, and will be marked as an answer.

A few of things:

$ Chronic.parse 'foo'

yields nil and not an exception.

$ Time.parse 'foo'

yields a Time object, not an exception. (Edit: In Ruby 1.8.7)

When you use a rescue, you need to specify the type of exception that you're rescuing

rescue SyntaxError, NameError => boom