I have a model User which has one to many relation to the Image model. 
How can I limit user to be able to store only 3 images?
I have a model User which has one to many relation to the Image model. 
How can I limit user to be able to store only 3 images?
How about validation?
class Image
  belongs_to :user
  validate :max_3_per_user
  # (...)
  private
  def max_3_per_user
    if user_id && Image.where(user_id: user_id).count >= 3
      errors.add(:images, 'There can only be 3 per user')
    end
  end
end