测验历史数据的题号迁移

db/migrate/20171012101648_migrate_exercise_question_num.rb

@@ -0,0 +1,17 @@
+class MigrateExerciseQuestionNum < ActiveRecord::Migration
+  def up
+    count = Exercise.all.count / 30 + 2
+    transaction do
+      for i in 1 ... count do i
+        Exercise.page(i).per(30).each do |exercise|
+          exercise.exercise_questions.reorder("created_at asc").each_with_index do |question, j|
+            question.update_column('question_number', j + 1)
+          end
+        end
+      end
+    end
+  end
+
+  def down
+  end
+end