Updating a Rails Association table - mysql

Question

I'm working on a quiz app in Rails that keeps track of a number of Facts
app/models/fact.rb
class Fact < ActiveRecord::Base
validates(:question, presence: true, uniqueness: { case_sensitive: false })
validates(:answer, presence: true)
end
Every time a user takes a new quiz, they generate an Exam
app/models/exam.rb
class Exam < ActiveRecord::Base
after_create :assign_facts
belongs_to :user
default_scope -> { order('created_at DESC') }
validates :user_id, presence: true
has_many :problems
has_many :facts, through: :problems
def assigned?(fact)
problems.find_by(fact_id: fact.id)
end
def assign!(fact)
problems.create!(fact_id: fact.id)
end
private
def assign_facts
facts = Fact.all.sample(10)
facts.each do |fact|
self.assign!(fact)
end
end
end
Since there are many Exams all using the same Facts, each Exam has_many Facts though an association table of Problems
app/models/problem.rb:
class Problem < ActiveRecord::Base
belongs_to :exam
belongs_to :fact
validates :exam_id, presence: true
validates :fact_id, presence: true
end
excerpt from db/scheme.rb:
create_table "problems", force: true do |t|
t.integer "exam_id"
t.integer "fact_id"
t.datetime "created_at"
t.datetime "updated_at"
t.boolean "correct", default: false
end
My problem is that I'm trying to figure out how to store the results of each user's exam (whether they answer a specific question either correctly, or incorrectly). I was planning on updating the association table each time the user answers a question and storing the result in the t.boolean "correct" collumn. This would be a fairly simple matter in PHP/MySQL (UPDATE problems SET correct = 1 WHERE exam = 'id' AND fact = 'id'), but I'm having difficulty figuring out how to do it the Rails way.
Is there some way I can simply, and easily update my associations table (problems) with Rails? OR Should I create a fourth table (maybe 'results' or something) to keep track of the user's correct/incorrect answers? --I know I don't have any controller code here, I'm just thinking out the broad strokes, and I want to keep things simple. Any help would be greatly appreciated.

Answer 1

You are almost there... you have already added a Boolean column called correct in the schema for the problem model, so now you just need to access that as an attribute when updating an Exam. Som somewhere in your controller code, you would say:
ps=#exam_taken.problems
ps.each do |p|
if answered_correctly(p)
p.correct=true
p.save
end
end
# This assumes you have a method that checks correctness inside the binding where the
# above code is written
#exam_taken.save
If you are using Rails3, you would have to also declare the correct attribute as attr_accessible in your model.
And here's a free pro-tip: Default scope is evil :)