Question

I am designing a vocabulary quiz application in ruby/rails.
I have basic model/association setup which will work, but i am worried about scalability.
There will be a set number of words in the application. For simplicity, lets say 100.
A user will be able to proceed to a question, which will be generated from looking at which questions they have had before. The question will provide a word and 4 choices for the definition (one being the definition, three other definitions being randomly chosen).

Here is the way my models and associations are set up currently;

class User < ActiveRecord::Base
  has_many :user_questions
end

class UserQuestion < ActiveRecord::Base
  belongs_to :user
  belongs_to :vocab_word
end

class VocabWord < ActiveRecord::base
  has_many :user_question
end

Assuming i were to keep this basic model, which of the following approaches should i use?

1. Have a set number of UserQuestion objects (100) per user and use
   calculated columns to store statistics the users performance on
   particular words. (e.g. user 502 has attempted the word ‘arid’ 3
   times and correctlty answered 2 times).
2. For each question
   attempt, create a new UserQuestion object. (e.g. user 502 attempted
   to guess ‘arid’ and was incorrect)

Are either of these approaches scalable? If the application had one million users, the first strategy would have 100 million rows in user_questions. the second could have much more than that.

Answer 1

You’re almost there. I would recommend extending your model with the following, plus the slight correction on UserQuestion and User association.

class User < ActiveRecord::Base
  has_and_belongs_to_many :user_questions
end

class UserQuestion < ActiveRecord::Base
  has_and_belongs_to_many :users
  belongs_to :vocab_word
end

class VocabWord < ActiveRecord::base
  has_many :user_question
end

class Attempt < ActiveRecord::base
  belongs_to :vocab_word
  belongs_to :user
  belongs_to :user_question

  attr_accessible :result
end

You’d need a user_questions_users association table to have a many-to-many association between questions and users. I believe it would be scalable. Make sure you set your indexes correctly.