Rails - Apr 2009 - routes, controllers, and intentions

I have the following tables: courses, students, and rosters.  The
rosters table references the courses and students tables.  With
default routes in place, to list the students in a course I would use:
http://localhost:3000/rosters/list

but this lists the rosters for all courses.

if I use http://localhost:3000/rosters/list/1

rails looks in the rosters table for entry with the id =1.  How do I
tell it I want all the entries where course_id = 1?

With default routing in place, it would seem to me to be something on 
the order of the following, given courses, students, and rosters:

course
   has_many rosters
   has_many students through rosters

student
  has_many rosters
  has_many courses through rosters

roster
  belongs_to course
  belongs_to student

-----
You need to pass the course_id to the roster in a param, like:

http://localhost:3000/rosters?course_id=1

which would allow a roster to determine which course it was for, and 
retrieve all the appropriate students.

def show
   @rosters = Roster.find(:all, :conditions => [''course_id =
?'',
params[:course_id]])
end

There are many other ways to organize and get at this information, such 
as a partial for the course ''show'' form, like 
''_course_students.html.erb'', which could just loop through the
@course.students collection to display the list of students.
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