ActiveRecord的：因爲它通過一個以上的其他關聯不能修改協會

Question

我不知道爲什麼這個協會是無效

class Tag < ActiveRecord::Base 
    has_and_belongs_to_many :routes 
end 

class Route < ActiveRecord::Base 
belongs_to :super_route 
has_and_belongs_to_many :tags 
end 

class SuperRoute < ActiveRecord::Base 
    has_one :route 
    has_many :tags, through: :route 
end 

然後，我希望能夠做到以下

s = SuperRoute.create 
s.route = Route.create 
s.tags << Tag.create 

除了這引發錯誤

ActiveRecord::HasManyThroughNestedAssociationsAreReadonly: Cannot modify association 'SuperRoute#tags' because it goes through more than one other association. 

什麼是這裏的根本性的錯誤？

Answer 1

class SuperRoute < ActiveRecord::Base 
    has_one :route 
    has_many :tags  #remove through: :route 
end