Custom order details fields

Hello,

I was wondering if anyone could help me regarding custom cart detail and order detail fields.  When adding a product to cart, I'm trying to also capture some custom fields that the user will input. These must be detail level fields and cannot be associated to the product through product custom fields or variations.

I was able to add the fields to the db through the API, but I'm having a hard time figuring out how to capture these fields when adding to cart.  This will be a custom add to cart button. Would it be best to simply add directly to the database, or is there a more elegant API call I can make? Any assistance would be appreciated.