Add timestamp columns to event_types

... required for Rails to calculate cache keys

db/migrate/20180226032958_add_created_at_and_updated_at_to_event_types.rb

@@ -0,0 +1,12 @@
+class AddCreatedAtAndUpdatedAtToEventTypes < ActiveRecord::Migration[5.0]
+  def up
+    add_column :event_types, :created_at, :datetime
+    add_column :event_types, :updated_at, :datetime
+    EventType.update_all(created_at: Time.now, updated_at: Time.now)
+  end
+
+  def down
+    remove_column :event_types, :created_at
+    remove_column :event_types, :updated_at
+  end
+end

db/schema.rb

@@ -233,6 +233,8 @@ ActiveRecord::Schema.define(version: 20180313012253) do
     t.string   "color"
     t.string   "description"
     t.integer  "program_id"
+    t.datetime "created_at"
+    t.datetime "updated_at"
   end
 
   create_table "event_users", force: :cascade do |t|