问题
I have 2 models (Workout, Equipment) in a has and belongs to many relationship. If I use Workout.find(:all, :joins => :equipment, :conditions => "equipment.id = 5") it works, but if I use Workout.find(:all, :joins => :equipment, :conditions => "equipment.id = null") it doesn't return the records with no association. Any ideas?
回答1:
Give this a whirl;
Workout.joins("left join equipments e on workouts.id = e.workouts_id").where("e.id is null")
来源：https://stackoverflow.com/questions/11279317/rails-habtm-find-all-records-with-no-association