Rails - May 2006 - HABTM - How do I do a select box for this?

I''ve got several habtm''s working fine in my app but have been
having
trouble with a new twist: imagine an app that tracks students and
courses that they''re taking.  So there''s a student Class and a
course
Class, and the tables also, and a students_courses table.  This stuff I
have down cold.

The problem was I wanted a form that allowed associating a student with
up to three courses, each individually selected from a drop-down select
box:

Student:  John
Course 1:  (select box)
Course 2: (select box)
Course 3: (select box)

I tried the following for my select box code in my view (this is
pseudo-code, I don''t have the source with me):

<% select :student, :course_id, Course.find(:all) %>

The error I''m getting is with the second parameter above.  I think
I''ve
got that wrong.  Is there any way to do what I''m doing?  I think the
problem is that I don''t understand how to modify a collection of many
courses when I''ve got three separate select boxes.  Thanks very much.

-- 
Posted via http://www.ruby-forum.com/.

If I understand you correctly, you want an admin page which gives three 
select boxes (preferably showing the course name) which you will use to 
populate your courses_students joining table upon posting.

I often want to create select boxes on admin pages, so I wrote a class 
function on the model which returned an array of arrays - [[name1, id1], 
[name2, id2], ...] etc. which I called ''options''. I passed
that into the
select helper function...


In app/models/course.rb:

class Course < ActiveRecord::Base
    def self.options
        options = []
        find(:all).each { |item|
            options += [[item.name, item.id]]
        }
        options
    end
end

and in my _form.rhtml file:

<%= select ''course'', ''course_id_1'',
@courses  %></p>


@courses comes from the controller:
 
  private
 
  def prepare_admin
    @courses = Genre.options
  end

This all seems over elaborate and weighty... ut it works nicely enough. 
I''m guessing there''s probably a helper function I
haven''t seen which
automates all this in the view layer only.

I could make the model function into a mixin by adding a little 
generic-ness... But I don''t know where to add it in as yet. Or I could 
add the functionality to all active records by adding it to the active 
record class.

It all seems a bit wonky though. It ''feels'' like I''m
creating display
information in the model layer, which doesn''t make me happy.

What''s the one-liner solution, guys?

Ben

Supplementary:

Once the select box is displaying (when I tried to use a .find, I just 
got a select box full of object serial numbers), you''ll need to:

1: Make sure the view is generating field names which aren''t the same
as
any in the student object. (course_id_1, course_id_2, etc.)
2: In the receiving controller, you will have to catch these by hand 
(params[:student_course_id_1] type of thing) and create new 
student_course type objects. Load them up with the values (if the course 
IDs are not nill), then save them.

I don''t think there''s an automatic way to do this, but
I''m new to all
this too. As you can probably tell.