Most proper way to use inherited classes with shared relations? - ruby-on-rails

Question

I have the TestVisual class that is inherited by the Game class :
class TestVisual < Game
include MongoMapper::Document
end
class Game
include MongoMapper::Document
belongs_to :maestra
key :incorrect, Integer
key :correct, Integer
key :time_to_complete, Integer
key :maestra_id, ObjectId
timestamps!
end
As you can see it belongs to Maestra.
So I can do Maestra.first.games which returns []
But I can not to Maestra.first.test_visuals because it returns undefined method test_visuals
Since I'm working specifically with TestVisuals, that is ideally what I would like to pull, but still have it share the attributes of its parent Game class.
Is this possible with Mongo. If it isn't or if it isn't necessary, is there any other better way to reach the TestVisual object from Maestra and still have it inherit Game ?

Answer 1

Single Collection Inheritance (SCI) in MongoMapper auto-generates selection,
ex., the following produce the same results.
p Game.where(_type: 'TestVisual').all
p TestVisual.all
See also mongomapper/lib/mongo_mapper/plugins/sci.rb - MongoMapper::Plugins::Sci::ClassMethods#query
However, MongoMapper does not auto-generate associations for subclasses based on the base class' associations,
and I don't think that this should be expected.
Note that SCI places subclasses and base classes in the same MongoDB collection.
If this is not what you want, you should consider other mechanisms for modularity.
You can define the following method yourself for an association accessor method, perhaps this is sufficient for your purposes?
For other association methods like append or push, the parent methods are probably workable.
class Maestra
include MongoMapper::Document
key :name, String
many :games
def test_visuals
games.where(_type: 'TestVisual')
end
end
test/unit/test_visual_test.rb
require 'test_helper'
def ppp(obj)
puts obj.inspect.gsub(/, ([^#])/, ",\n\t\\1").gsub(/, #/, ",\n #")
end
class TestVisualTest < ActiveSupport::TestCase
def setup
Maestra.delete_all
Game.delete_all
end
test "inheritance" do
maestra = Maestra.create(name: 'Fiona')
maestra.games << Game.create(incorrect: 1, correct: 9, time_to_complete: 60)
maestra.games << TestVisual.create(incorrect: 2, correct: 8, time_to_complete: 61)
ppp maestra.games.to_a
ppp maestra.test_visuals.to_a
end
end
output
Run options: --name=test_inheritance
# Running tests:
[#<Game _id: BSON::ObjectId('4ff7029a7f11ba6e43000002'),
_type: "Game",
correct: 9,
created_at: Fri,
06 Jul 2012 15:22:02 UTC +00:00,
incorrect: 1,
maestra_id: BSON::ObjectId('4ff7029a7f11ba6e43000001'),
time_to_complete: 60,
updated_at: Fri,
06 Jul 2012 15:22:02 UTC +00:00>,
#<TestVisual _id: BSON::ObjectId('4ff7029a7f11ba6e43000003'),
_type: "TestVisual",
correct: 8,
created_at: Fri,
06 Jul 2012 15:22:02 UTC +00:00,
incorrect: 2,
maestra_id: BSON::ObjectId('4ff7029a7f11ba6e43000001'),
time_to_complete: 61,
updated_at: Fri,
06 Jul 2012 15:22:02 UTC +00:00>]
[#<TestVisual _id: BSON::ObjectId('4ff7029a7f11ba6e43000003'),
_type: "TestVisual",
correct: 8,
created_at: Fri,
06 Jul 2012 15:22:02 UTC +00:00,
incorrect: 2,
maestra_id: BSON::ObjectId('4ff7029a7f11ba6e43000001'),
time_to_complete: 61,
updated_at: Fri,
06 Jul 2012 15:22:02 UTC +00:00>]
.
Finished tests in 0.026661s, 37.5080 tests/s, 0.0000 assertions/s.
1 tests, 0 assertions, 0 failures, 0 errors, 0 skips