Hi! I'm a newbie wrapping my head around the Rails way of designing apps 
at the database layer, and I've hit a minor conceptual logjam and was 
hoping some of you might be able to help work me through it.

I'm (re)designing a PHP audio jukebox in RoR (I'm going to be migrating 
a big pile of data from a system called Netjuke, which has been folded 
into the Jinzora project). I have some very definite ideas about how the 
data ought to be structured and how relationships ought to work, and the 
metadata schema I've designed generates lots of complicated dependencies 
and relationships which I feel are best specified and enforced at the 
database level. For now I'm working in PostgreSQL, but I might move this 
all over to Oracle at some point.

So my toy version of the app has three classes of entities: artists, 
albums and tracks. Albums and tracks belong to artists (think 
compilations or soundtracks for why that notion of ownership needs to be 
at both levels) and tracks also belong to albums. I'm building the 
schema via migrations, but have slapped in migrations that look like:

class AddConstraints < ActiveRecord::Migration
  def self.up
    execute 'ALTER TABLE tracks ADD FOREIGN KEY(album_id) REFERENCES 
albums ON DELETE RESTRICT'
    execute 'ALTER TABLE tracks ADD FOREIGN KEY(artist_id) REFERENCES 
artists ON DELETE RESTRICT'
    execute 'ALTER TABLE albums ADD FOREIGN KEY(artist_id) REFERENCES 
artists ON DELETE RESTRICT'
  end

  def self.down
    execute 'ALTER TABLE tracks DROP CONSTRAINT tracks_artist_id_fkey'
    execute 'ALTER TABLE tracks DROP CONSTRAINT tracks_album_id_fkey'
    execute 'ALTER TABLE albums DROP CONSTRAINT albums_artist_id_fkey'
  end
end

My problem is that using fixtures and transactional unit tests, I have 
to incorporate all the fixtures for the classes in the foreign key 
restrictions to ensure that fixtures get set up and torn down correctly. 
I.e. unless I have a line that says "fixtures :artists, :albums, 
:tracks" in test/unit/(album|artist|track)_test.rb, the test database 
isn't left in a sane state across unit tests and unit tests start 
failing due to integrity constraint errors when the fixture code tries 
to empty out the table during the fixture setup invoked by the fixtures 
method.

It was a bit of an effort to figure all that out, and my solution feels 
hacky. Why should I have to set up fixtures for tracks and albums when 
I'm only testing artists, who sit at the top of this hierarchy? And 
how's that going to play when I add in many-to-many relationships 
between groups (artists) and their members? And glom genres onto this? 
It seems like this is going to make my test cases increasingly complex 
and unwieldy.

Is it already time for me to abandon using "fixtures" in my test cases 
and start doing explicit fixture setup and teardown? Or is there a 
simple way I can modify the framework, e.g. to automatically clear out 
all of the fixtures used by an individual test case? I can't imagine I'm 
the only person who's run into this.

Thanks in advance to any insight you might be able to provide. RoR is 
totally making it fun for me to work on this project again, and for that 
alone I'm very thankful.

Forrest

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