attachment history中description字段类型修改

db/migrate/20161015013348_change_description_for_attachment_history.rb

@@ -0,0 +1,9 @@
+class ChangeDescriptionForAttachmentHistory < ActiveRecord::Migration
+  def up
+    change_column :attachment_histories, :description, :text
+  end
+
+  def down
+    change_column :attachment_histories, :description, :string
+  end
+end