Software development topics I've changed my mind on

> ORMs are the devil in all languages and all implementations. Just write the damn SQL

What are the main issues people run into with ORMs? I've used Django ORM for years and written some relatively large applications using it without much problems. Complex queries and aggregations can result in quite hairy code though.

I've seen and poked at a lot of the ORM-hating on here, and whenever I can get people to give specific examples instead of generic theory-level stuff, it's either not a problem in Django or Django has a fix you just need to learn about and use. The fixes have sometimes even been there for over a decade. It seems be leaps and bounds ahead of every other ORM out there.

The main problem is if you are not very careful it leaks its internals (ie. the relational model) into everything it touches. That's what the N+1 query problem is. Business logic shouldn't have to know that certain attributes will cause database queries. By carefully writing managers and having a rule to never use querysets anywhere else you can avoid it, but it requires everyone to understand this and all the Django docs and examples everywhere will just randomly drop a queryset into a view or do a `prefetch_related` because they know that some higher-level function is going to need access to that attribute (ie. coupling code together).

Ultimately Django just doesn't fully do the object-relational mapping. It maps single rows, but that's it. So it doesn't really support objects that contain lists or sets etc. Things like SQLAlchemy can actually map data from a relational database into plain old objects. Those objects can be instantiated (e.g. in tests) completely independently of the database. Notice how in Django you can't test anything without a database being present? Why do I need to store an object in a db just to test some method on an entity?

The default test runner creates the test database automatically yes, but you can create Django model objects without touching the database, just use the class like a constructor and don't save it: Person(name="Foo", age=30)