`QuerySet.select_related()` and `QuerySet.prefetch_related()` are the bread and butter of Django query optimisation. I think most of the time that I've noticed a performance issue in our code, it's been easily fixed with one of those.
Django's ORM gets a lot of flak, but I don't remember the last time I had complex queries that I could not do with
it.
You still need to understand a minimum of SQL and databases, and usually those that complain about the ORM are the ones that expect it to be a "sufficiently advanced compiler", but it has matured so much that nowadays the developers consider a *bug* every time the answer to How do I do this query X? involves something along the lines of use .extra or raw sql.
This is true, though to be fair to the critics, the syntax through which you express these complex queries is often clunky and unintuitive. For example, I need to re-read the documentation every time I use the annotation API because it's generally not obvious how to use it, and I've run into a few edge cases where you need extra code/syntax just to deal with its nuances and ambiguities.
Even though Django has come a long way, I greatly prefer ORMs like SQLAlchemy and Ecto that map more closely to the SQL query I'm trying to write.
