在rails中循环通过fixnum

Question

I have an examscore model with the following columns:

academic_year_id, grade_id, student_id, subject_id, total_score

and an averagescore model with these columns:

academic_year_id, grade_id, student_id, average

My requirement is to iterate through the Examscore model by academic_year_id and grade_id , and calculate the average score of each student for all subjects taken by the student (ie sum total score of all subjects divided by the number of subjects) then store the average in the AverageScore model. I am finding this difficult and any help will be very much appreciated.

What I have done so far is:

total = 0
counter = 0 
scores = Examscore.where(:academic_year_id => 3, :grade_id => 4)
scores.each do |std|
  std.student_id.each do |tot|
  total += tot.total_score 
  counter += 1
end
puts total.fdiv(counter)

but it fails because std.student_id is a Fixnum not an Array .

Any guidance on how to approach this please?

Answer 1

As this is some sort of school project, I'm assuming the tables are not that big. Therefore, this should do the trick:

scores = Examscore.where(academic_year_id: 3, grade_id: 4)

scores.group_by(&:student_id).each do |student_id, examscores|
  average = examscores.sum(&:total_score) / examscores.size.to_f
  AverageScore.create academic_year_id: 3, grade_id: 4,
                      student_id: student_id, average: average
end