Selecting Things in All of the Nominated Categories

I came across a problem this week, that I was sure, had a canonical solution (i.e. standard and documented). But no, not that I could find. So yet again a process of reading, searching, testing, trying, talking (on Stack Overflow, with ChatGPT) and resulting notes and even a sandbox (demo).

Problem Statement

The context: A database (nominally behind a website) containing Things, and those Things are in Categories.

The environment: Django as a web framework and Python as …

canonical chatgpt demo django notes overflow process python reading searching solution sql stack stack overflow standard testing webdev