i am trying to get the time passed from the moment i posted a thing till now . I am defining a method in my model class :

```
class Post < ActiveRecord::Base
validates :comment , :presence => true

def time_past
 DateTime.now - self.created_at

end
end

```

Here is the error :

irb(main):001:0> Post.first.time\_past
TypeError: expected numeric or date
 from /usr/lib/ruby/1.8/date.rb:1252:in `minus_without_duration'
 from /usr/lib/ruby/gems/1.8/gems/activesupport-3.0.3/lib/active_support/core_ext/date/calculations.rb:98:in`-'
 from /home/badescuga/proiecte/soundplace/app/models/post.rb:5:in `time\_past'
 from (irb):1