Rails query using HMTH and multiple join models

I am using Rails 3 and wanted to get the classes a student has access to based upon the model below

class Student
    has_many :students_levels
    has_many :levels, :through => :students_levels
    end

    class Class
    has_many :classes_levels
    has_many :levels, :through => :classes_levels 
    end

    class Level
    has_many :students_levels
    has_many :classes_levels
    end

    class StudentsLevel 
    belongs_to :students
    belongs_to :levels
    end
    class ClassesLevel
    belongs_to :classes
    belongs_to :levels
    end

I came up with the query below but didn't think it seemed like the best Rails way to do things and开发者_StackOverflow社区 wanted to get additional suggestions. Thx

Class.where(:id => (ClassesLevel.where(:level_id => Student.find(1).levels)))

I want to add this as an instance method to Student and was thinking there would be a better way doing something with has many through.

I quite did not understand the whole logic behind your class structure. Why you are not connecting students directly into a class? And how a class can have many levels. I mean if you have Math1 and Math2, those are different classes, right? Or do you have Math1,2,3?

Well, anyway, here's the solution if you want to use current assosiations, I hope it suites your needs:

 Class Student      
 ...
 def available_classes
    Class.find(:all, 
      :include => {:levels => {:students_levels => :student}}, 
      :conditions => ["students.id = ?", self.id])
  end

And sorry, this is still in Rails 2.x format...