Rails scope: association is nil

Question

In my Rails app, projects can have videos. I want to create a scope for the Project to grab projects that do not have a video associated with it. How do I do this?

Here are my model associations

class Project < ActiveRecord::Base
  has_one :video
end

class Video < ActiveRecord::Base
    belongs_to :project
end

Answer 1

Just faced this right now, and this has worked for me:

Project.includes(:video).where(videos: { id: nil })

The trick is to use the singular in includes and the plural in where

Answer 2

building off of messanjah's answer, the way you would turn that into a scope is the following:

class Project < ActiveRecord::Base
  has_one :video
  scope :videoless, -> { left_joins(:videos).where("videos.id IS NULL") }
end

class Video < ActiveRecord::Base
  belongs_to :project
end