学时迁移成整数

db/migrate/20190815064541_modify_class_period_for_courses.rb

@@ -0,0 +1,5 @@
+class ModifyClassPeriodForCourses < ActiveRecord::Migration[5.2]
+  def change
+    change_column :courses, :class_period, :integer, :default => 0
+  end
+end