Question

I have a Reservation model that takes an appointment attribute as date and has a virtual attribute duration that indicates how long the appointment will take. The real attribute, booking_end takes a Time that is referenced all over my application. However, for ease of input, we use duration instead of choosing another Time. The fields are below:

def duration
  ( (booking_end - date) / 1.hour ).round( 2 ) rescue nil
end

def duration=(temp)
  if ( true if Float(temp) rescue false )
    self.booking_end = time_round(date + temp.to_f.hours, 15.minutes)
  else  
    errors.add(:duration, "must be a number, stated in hours.")
    self.booking_end = nil
  end
end

The whole thing fails when I reference the date field while creating a new record. I get a ‘nil’ error because date hasn’t been initialized. How can I fix this problem? The rest of this works when updating existing records.

Answer 1

When you call Reservation.new(:date => date, :duration => duration) ActiveRecord::Base assigns attributes values this way (see assign_attributes method):

attributes.each do |k, v|
  ...
  respond_to?("#{k}=") ? send("#{k}="", v) 
  ...

Hash#each method iterates through the values the way that :duration key is accessed before :date one, so date is nil inside the duration= method:

ruby-1.8.7-p302 > {:date => Date.today, :duration => 5}.each do |key,value|
ruby-1.8.7-p302 >     puts "#{key} = #{value}"
ruby-1.8.7-p302 ?>  end
duration = 5
date = 2010-11-17

So you’ll have to call duration= after initialization.

Or you can redefine Reservation#initialize to call super with :date and then update_attributes with the rest of parameters.