Activerecord conditions and named scope - undefined method `created_at'

Subscriber  
has_and_belongs_to_many :skills. 

Skill   
has_many :positions

in subscriber.rb:

scope :notify_today, 
      includes(:skills => :positions).
 开发者_如何学Python     where("positions.created_at > ? AND positions.created_at > ?", 
             1.day.ago, self.created_at)

Basically I want to find all subscribers that have positions 1) created 1.day.ago AND 2) created after the subscriber

The error occurs because the class of self here is Class, not Subscriber, as is wanted.

As a solution, you can make a lamda like this and pass in the parameter for created_at: (I presume your scope is working otherwise, because I have not tested this with your scope code specifically)

scope :notify_today, 
      lambda { |created_at| includes(:skills => :positions).
      where("positions.created_at > ? AND positions.created_at > ?", 
             1.day.ago, created_at) }

And use it:

@subscribers = notify_today(Time.now)