Issue with 0:Fixnum

full_trace.rb

rake aborted!
undefined method `to_d' for 0:Fixnum
C:/teststore/app/models/product.rb:55:in `shipping_cost='
C:/teststore/app/models/product.rb:126:in `default_to_zero_if_necessary'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/active_support/callbacks.rb:396:in `_run_validation_callbacks'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/active_support/callbacks.rb:81:in `run_callbacks'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activemodel-3.1.0/lib/active_model/validations/callbacks.rb:53:in `run_validations!'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activemodel-3.1.0/lib/active_model/validations.rb:179:in `valid?'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/validations.rb:69:in `valid?'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/validations.rb:77:in `perform_validations'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/validations.rb:50:in `save'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/attribute_methods/dirty.rb:22:in `save'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/transactions.rb:241:in `block (2 levels) in save'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/transactions.rb:295:in `block in with_transaction_returning_status'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/connection_adapters/abstract/database_statements.rb:192:in `transaction'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/transactions.rb:208:in `transaction'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/transactions.rb:293:in `with_transaction_returning_status'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/transactions.rb:241:in `block in save'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/transactions.rb:252:in `rollback_active_record_state!'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/transactions.rb:240:in `save'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/has_many_association.rb:16:in `insert_record'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:421:in `block (2 levels) in create_record'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:333:in `add_to_target'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:419:in `block in create_record'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:143:in `block in transaction'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/connection_adapters/abstract/database_statements.rb:192:in `transaction'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/transactions.rb:208:in `transaction'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:142:in `transaction'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:418:in `create_record'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:416:in `block in create_record'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:416:in `collect'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:416:in `create_record'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:107:in `create'
c:in `create'
C:/teststore/db/seeds.rb:35:in `<top (required)>'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:234:in `load'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:234:in `block in load'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:223:in `block in load_dependency'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:640:in `new_constants_in'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:223:in `load_dependency'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:234:in `load'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/engine.rb:487:in `load_seed'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/railties/databases.rake:299:in `block (2 levels) in <top (required)>'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:636:in `call'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:636:in `block in execute'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:631:in `each'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:631:in `execute'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:597:in `block in invoke_with_call_chain'
c:/Ruby192/lib/ruby/1.9.1/monitor.rb:201:in `mon_synchronize'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:583:in `invoke'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2051:in `invoke_task'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2029:in `block (2 levels) in top_level'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2029:in `each'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2029:in `block in top_level'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2023:in `top_level'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2001:in `block in run'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:1998:in `run'
c:/Ruby192/lib/ruby/gems/1.9.1/gems/rake-0.8.7/bin/rake:31:in `<top (required)>'
c:/Ruby192/bin/rake:19:in `load'
c:/Ruby192/bin/rake:19:in `<main>'

Product.rb

class Product < ActiveRecord::Base
  attr_accessible :cost, :purchase_date, :link, :store_id, :tax_rate, :shipping_cost, :cost_per_unit, :unit, :unit_amount
  belongs_to :user
  belongs_to :store
  validates_presence_of :store
  after_save { |up| up.destroy if up.store.blank?}
  before_validation :default_to_zero_if_necessary, :on => :create
  
  UNITS = ["seconds", "days", "hours", "weeks", 'years', "feet", 'inches', 'pounds', "kilograms", 'grams',
    'metres', 'centimetres', 'milimetres', 'gallons', 'quarts', 'cups', 'pints', "cubic feet", "cubic inches", "cubic metres", "fluid ounces", 'pieces', "parts"]
  validates_inclusion_of :unit, :in => UNITS, :allow_blank => true

  def shipping_cost=(num)
    num.gsub!(',','') if num.is_a?(String)
    self[:shipping_cost] = num.to_d
  end
  
  def cost=(num)
    num.gsub!(',','') if num.is_a?(String)
    self[:cost] = num.to_d
  end
  
  def tax_rate=(num)
    num.gsub!(',','') if num.is_a?(String)
    self[:tax_rate] = num.to_d
  end
  
  def cost_per_unit=(num)
    num.gsub!(',','') if num.is_a?(String)
    self[:cost_per_unit] = num.to_d
  end
  
  def unit_amount=(num)
    num.gsub!(',','') if num.is_a?(String)
    self[:unit_amount] = num.to_d
  end

  private

  def default_to_zero_if_necessary
    self.tax_rate = 0 if self.tax_rate.blank?
    self.shipping_cost = 0 if self.shipping_cost.blank?
    self.cost = 0 if self.cost.blank?
    self.cost_per_unit = 0 if self.cost_per_unit.blank?
    self.unit_amount = 0 if self.unit_amount.blank?
  end
end