删除has_many的正确方法:通过连接记录?

class Post < ActiveRecord::Base
  has_many :posts_tags
  has_many :tags, through: :posts_tags
end

class PostsTag < ActiveRecord::Base
  belongs_to :post
  belongs_to :tag
end

class Tag < ActiveRecord::Base
  has_many :posts_tags
  has_many :posts, through: :posts_tags
end
class Post < ActiveRecord::Base
  has_many :pos