[Answer]-Django multi-criteria weighted rating

The easiest solution for the weighted rating would be to add an additional field and populate it automatically in a custom save method on the rating object.

As far as getting the overall average rating goes, you can either calculate it dynamically every time it’s needed (easiest/most accurate method) using Django’s aggregation queries, or you can try to maintain an average rating field that is updated each time a rating is added/deleted/updated (the more performant method if you’re running a read-heavy service). See my answer here for more details on implementing these (using sums rather than averages) and more detail on the tradeoffs.