Types for objects instances seem incorrect about piccolo

[dantownsend]

@dbanty Yeah, this is something I want to get sorted.

I want Piccolo to work really well with MyPy, and this is the main pain point at the moment.

I'll try using typing.cast in Table.__init__ to see if that helps.

[dbanty]

I assume it'll be difficult because you'll either lose type annotations with the query syntax (I assume that Column == value in a .where returns something that the .where expects and not a bunch of bools) or end up with Unions at run time. This is a larger issue in general with ORMs I think since the Table definition is the same class as the Result but the types of the attributes are, by definition, different.

I'm pretty sure that the way sqlalchemy-stubs deals with this is with their mypy plugin so you might end up having to go down this route as well.

You could maybe make each Column type subclass their runtime counterpart? A bit hacky since it won't necessarily be true.

Another possible option would be to design database schemas more like how Pydantic defines theirs? Where the type annotation is used for each field and you can set it to a Field which I believe just returns Any so mypy ignores it? That might take some rework though in the API and therefore potentially breaking changes.

Lots to think about. I'm always happy to discuss and bounce ideas around, especially if it helps lead to a better ORM for the Python ecosystem 😁