Validation doesn't work (Rails 3)

Question

In model/item.rb I have custom validation method

  validate :double_dates
  after_save :double_check

  private

  def double_dates
    if Item.where(:user_id => self.user_id, :asin => self.asin, :domain => self.domain).where("DATE(created_at) = ?", Date.today).length >= 1
      errors.add(:created_at, "no double dates")
    end

Validation method does work in "rails c". But, when I run two task at the same time (rails runner "ApplicationController.rotate" I have Item.save in rotate method) - validation stops working.

irb(main):044:0> i1.created_at
=> Thu, 24 Apr 2014 02:41:15 UTC +00:00
irb(main):045:0> i2.created_at
=> Thu, 24 Apr 2014 02:41:15 UTC +00:00
irb(main):046:0> i1.created_at == i2.created_at
=> false
irb(main):047:0> i1.created_at.to_time.to_i == i2.created_at.to_time.to_i
=> true
irb(main):048:0> i1.created_at.class
=> ActiveSupport::TimeWithZone
irb(main):049:0> i2.created_at.class
=> ActiveSupport::TimeWithZone
irb(main):050:0> i1.created_at.usec => 311714 
irb(main):051:0> i2.created_at.usec => 312779 

Any hints or advice would be appreciated.

Answer 1

Thanks to @FabKremer I was able to solve it :)

by adding @i.created_at = Time.now.change(usec: 0) before Item.save :)

Nevertheless I'm accepting his answer, cuz it'll work for most cases.

Answer 2

I had a similar problem once, and guess you could actually solve this problem adding indexes to the table. Add an index to the created_at column in Items.

Here you've got a full explanation about indexing in rails.

Hope it helps!