rails中的模型遍历:从子级到兄弟级的子级

class Advisor < ActiveRecord::Base
  belongs_to :course
end

class Course < ActiveRecord::Base
  has_many :advisors
  has_many :sessions
  has_many :materials, :through=>:sessions
end

class Session < ActiveRecord::Base
  belongs_to :course
  has_many :materials
end

class Material < ActiveRecord::Base
  belongs_to :session
end

一、 每个导师教一门课,每门课都有课,每节课都有材料。 我想从一个顾问到所有相关材料,例如: Advisor.first.materials

class Advisor < ActiveRecord::Base
  belongs_to :course
  has_many :sessions, :through=>:course
  has_many :materials, :through=>:sessions
end

但它没有起作用,因为它将会话视为多对多表: Unknown column 'sessions.advisor_id' in 'where clause': SELECT 'material'.* FROM 'materials' INNER JOIN 'sessions' ON 'materials'.session_id = 'sessions'.id WHERE (('sessions'.advisor_id = 1))

然后我试着做:

class Advisor < ActiveRecord::Base
  belongs_to :course
  has_many :materials, :through=>:course
end

试图让协会在“课程”模式中使用“材料”协会,但收到:

ActiveRecord::HasManyThroughSourceAssociationMacroError: Invalid source reflection on macro :has_many :through for has_many :materials, :through=>:sessions.  Use :source to specify the source reflection.

尝试使用“会话”作为源,这是一个很好的尝试,但使我只收到会话,而不是材料。

如果有可能的话有什么想法吗? 我正在使用Rails 2.3.8(也许是时候升级了?)

谢谢! 阿米特