Rails form select helper populated in edit

In an existing codebase, one attribute of the `discount` model is `discount_type`. Since there are only 2 types of discounts (percentage and cash) used in this system, they are hardcoded as `percentage` or `cash` throughout the system, there is no `discount_types` table or anything to map to. In the form, there is the following code: ``` =form_for @discount do |f| ... =f.select :discount_type, options_for_select(["percentage", "cash"]) ... ``` This works great for new discounts, but when pulling up the form to edit a discount, `percentage` is always selected, no matter what the `discount` object's `discount_type` is. How do we get the form to default to the `discount_type` of the object being edited?