nested with scope problem

hello there,
im a beginner in ruby on rails.

i have 3 tables:
timetable --contains--> id, class1_id, subject_id, etc
student --contains--> id, class1_id, etc
class1 --contains--> id, classname

now, i wanted to view student's timetable..
so, i think.. table timetable must retrieve student's class1_id from
table student.
please help me to settle this.

i tried something like this but it cannot be run.. im lack of idea
already:
def timetable
@stud_ttable = Student.find(:first, :conditions => ["class1_id = ?",
student.class1_id])
@timetables = Timetable.find(:all, :conditions => ["class1_id = ?",
@stud_ttable.id])
end

I think you'd be better off with using either has_many, perhaps with
the :through option.

students table has id and attributes about the student, NO classx ids.

courses table (I'm assuming you were trying to model the first class
in the student's schedule with the name class1, don't do that, I chose
courses so that the model class name doesn't conflict with the Ruby
Class class). Has id and attributes about the course..

Now two options. 1st and simplest.

courses_students table has class_id and student_id fields

class Student < ActiveRecord::Base
   has_and_belongs_to_many :courses
end

class Course < ActiveRecord::Base
  has_and_belongs_to many: students
end

Or if you want to have attributes associated with a particular
enrollment of a student in a course.

instead of the courses_student table have, say, a course_enrollment table with
id, student_id, course_id and any other attributes needed for the enrollment.

Now

class Student < ActiveRecord::Base
    has_many :course_enrollments
    has_many :courses :through => :course_enrollments
end

class Course < ActiveRecord::Base
   has_many :course_enrollments
   has_many :students :through => :course_enrollments
end

class Course_Enrollment < ActiveRecord::Base
   belongs_to :student
   belongs_to :course
end