[cdcarter]

I think the poster is specifically referring to using inheritance in Django ORM, where if you had e.g. a model Book and then a model Novel that inherits from it. In python these are modeled as a class inheritance hierarchy, and Django (at least, by default) creates a database table per class in the hierarchy. If you have 3-4 levels of inheritance, that's 3-4 extra joins per query.

[pmontra]

This. That customer of mine started a project a few years before hiring me. They used inheritance and each model is scattered around a number of tables. No external tool can sensibly access that database, except that very Django app and its manage.py commands. Add a similarly enthusiastic use of apps under the same main directory and the database is a mess of long named tables with a tangle of relationships between them.

We started another project later on and we planned the database first. We wrote one model per table, no inheritance, only a few cleanly delimited apps. We still use makemigrations and migrate but if we want we can write a piece of software on any language to access that database.

[mixmastamyk]

We use that, a base model and some mixins, but we use Meta.abstract=True (or similar, not at my desk) on the parents and have not noticed any issues, though have not looked for them either! Should I be concerned?

[cdcarter]

That works fine. It's when you inherit from a non-abstract model that you end up with the trickier data model.

[riffraff]

Oh, got it thanks