Model relation issue with Ruby on Rails

Question

I have a few models:

class StatsParent < ActiveRecord::Base
class CourseStat < StatsParent
class PlayerCourseStat < CourseStat

I have the Course model set up as such:

class Course < ActiveRecord::Base
  has_one  :course_stat
  has_many :player_course_stats

  def update_stats(plyr_rnd)
    puts self.course_stat  # this puts #<PlayerCourseStat:0x000001015c54e0>
    if self.course_stat
      self.course_stat.add_player_round(plyr_rnd)
    else
      self.course_stat = CourseStat.new(plyr_rnd)
    end
  end
#...rest of the class

The issue I am running into: In the course I check to see if the course_stat exists and if it doesn't to create it. But in the model it is saying that it exists because there is a player_course_stat associated with this instance.

When I dive into the ruby script/console and check to see the course_stat relationship it is nil.

> ruby script/console
Loading development environment (Rails 2.3.3)
>> course = Course.find(1)
=> #<Course id: ...>
>> course.course_stat
=> nil
>> course.player_course_stats
=> [#<PlayerCourseStat id: 1, ...>]

1. Is there a problem with the way I have the relationships for the Course model set?
2. Why is course_stat nil in the console but not in the application as it is running?

Update:

Looking into this a bit further I looked through the logs to get the SQL statements that are generated for the console and the application.

# from console: course.course_stat
CourseStat Load (0.2ms)   SELECT * FROM "stats_parents" WHERE 
("stats_parents".course_id = 1) AND ( ("stats_parents"."type" = 'CourseStat' ) ) 
LIMIT 1

# from app: course.course_stat
CourseStat Load (0.3ms)   SELECT * FROM "stats_parents" WHERE 
("stats_parents".course_id = 3) AND ( ("stats_parents"."type" = 'CourseStat' OR
                                       "stats_parents"."type" = 'PlayerCourseStat' ) ) 
LIMIT 1

I want a query like the console creates to be used. Is there a way for me to do this with out having to write the sql out in full?

Answer 1

Given your relationships:

class StatsParent < ActiveRecord::Base
class CourseStat < StatsParent
class PlayerCourseStat < CourseStat

when you have a PlayerCourseStat, you have a Course stat because you've modeled an IS-A relationship... a PlayerCourseStat IS-A CourseStat. Did you mean to do:

class PlayerCourseStat < StatsParent

Answer 2

I think you should simply add a condition to your has_one

has_one :course_stat, :conditions => "type = 'CourseStat'"

It seems redundant, but I find the inconsistency between console and the app to be very confusing...

Answer 3

If you want to keep this simple (which is always a nice idea), eliminate the inheritance and put the shared logic in a module

module Stats
  def ...
end

class CourseStat < ActiveRecord::Base
  include Stats
end

class PlayerCourseStat < ActiveRecord::Base
  include Stats
end