From: Ohad Lutzky <lutzky@...>
Date: 2006-10-14T09:09:12+09:00
Subject: Backwards references in arrays of arrays of...

I'm creating a scheduling application for my university, the Technion. 
The course data we receive in a file called a REP file, which my 
application parses. Its essential, simplified structure is this:

Faculties (which have names) contain courses
Courses (which have numbers and names) contain groups
Groups (which have numbers and lecturer names) contain events
Events have days, start/end times, and locations

This data I convert once (it takes a while), and then Marshal it. I 
don't use YAML, though I'd rather do that, because of a unicode bug in 
the stable version. The choice between them is less relevant.

So in my program, the data is stored as an array of Faculty objects, 
which have a courses property which is an array of Course objects, and 
so on - all the way down to events.

Now, I display the rendered schedule using Gecko. I have prepared an 
HTML template for this, for which all I have to add is event lines in 
Javascript, which go something like this:

addEvent(course_id, day, start, end, desc);

This code is then inserted into the HTML, which goes about the 
rendering. course_id should be a unique identifier for color-coding. 
desc, which is the actual rendered text, should contain the event's 
course name & number, group number, lecturer, and location.

Now here's the kicker - an event doesn't know all that. It knows its 
day, start/end time, and location. And that it's an event. It doesn't 
know what group it's a part of, what course, nothing.

So the question is - how do I generate the javascript?

Currently, the scheduler returns an array of arrays of groups (an array 
of groups per course). So my options are

- Have the scheduler generate the javascript - let it figure out which 
groups belong to which courses, iterate down to the choices, and 
generate everything
- Store javascript strings within the events during parsing of the REP 
file
  (I don't like this because if I use YAML later on, I'd like it to be
  redistributable instead of the REP file, and that's, well, icky)
- Store back-references to the group and course within the event - ruby
  seems to handle this gracefully, with appropriate links in the YAML 
file
  etc. (no infinite recursion). To get a feel for what I mean, try

  LinkBack = Struct.new(:link)
  => LinkBack
  l = LinkBack.new
  => #<struct LinkBack link=nil>
  l.link = l
  => #<struct LinkBack link=#<struct LinkBack:...>>
  y l
  --- &id001 !ruby/struct:LinkBack
  link: *id001
  => nil

  Once these are in, it's pretty simple to generate the javascript code
  from within the Event.
- ...or something else I haven't thought of. What do you guys think?

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