Good example of CRUD

Would this considered a good example for CRUD in CI4?

https://makitweb.com/crud-create-read-up...igniter-4/

What I'm after, at the moment, is the differences between Create and Update. I have creating (new) entries working, I have view (existing) entries working, but for some reason I can't seem to nail down Edit/Update. I'm trying to use the same function ("edit") in my controller for Create and Edit. If it's a GET request, and the record ID is set, I assume we're editing, so I read the record from DB. If it's a POST request, I validate (and possibly save/update). But I can't seem to populate the form properly in the controller.
Creating and saving is not a problem.

-joho