默认值修改

db/migrate/20190815064541_modify_class_period_for_courses.rb

@@ -3,6 +3,6 @@ class ModifyClassPeriodForCourses < ActiveRecord::Migration[5.2]
     Course.find_each do |c|
       c.update_column(:class_period, c.class_period.to_i)
     end
-    change_column :courses, :class_period, :integer, :default => 0
+    change_column :courses, :class_period, :integer
   end
 end