课堂分班的迁移

db/migrate/20190829084147_migrate_course_group_position.rb

@@ -0,0 +1,11 @@
+class MigrateCourseGroupPosition < ActiveRecord::Migration[5.2]
+  def change
+    Course.all.each do |course|
+      if course.course_groups.exists?(position: 0)
+        course.course_groups.each_with_index do |group, index|
+          group.update_attributes(position: index+1)
+        end
+      end
+    end
+  end
+end