How do I fix the return type of a Django model manager's method?

Question

I’m using Django 4.1.7 with django-stubs 1.16.0, and mypy 1.1.1.

I have code that looks like this:

class ProductQuerySet(QuerySet):
    ...

class ProductManager(Manager):
    def create_red_product(self, **kwargs) -> "Product":
        return self.model(color=Product.Color.RED, **kwargs)

_product_manager = ProductManager.from_queryset(ProductQuerySet)

class Product(Model):
    ...
    objects = _product_manager()

When mypy looks at this, it says:

models/product.py:46: error: Incompatible return value type (got "_T", expected "Product")  [return-value]

It seems like the type of self.model in a model manager method is _T, which from what I understand is a generic type bound to the model, which in my case should be "Product".

Why isn’t this working? How can I fix it?

Asked By: John

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Source

Answer 1

I can’t reproduce one to one your case, but please try to specify what exactly your manager is for by:

class ProductManager(Manager["Product"]):

Answered By: Jaroszewski Piotr

How do I fix the return type of a Django model manager's method?

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