How to do typing in django model field?-CodePudding

With the recent addition of inlay types for python in VS Code I noticed that the typing for a Field will look like this:

As you can see it is Field[Unknown, Unknown]. And as you know if you don't provide a type to a field, you won't get attribute hints for the field, and the field will be shown as Unknown. You could just provide an str type if you for example have a CharField, something like this:

field: str = models.CharField()

The problem is, if you want to use a strongly typed linter - it will show you an error, that the assigned value is not of type str.

So I saw this inlay and I started playing around with this generic, and I noticed that the second parameter of the generic will be the type used to represent the field attribute:

My question is, does anyone know what is the first parameter of the generic used for, and where is this generic even created, because inside of the package I see that the Field class does not inherit any Generics.

CodePudding user response：

Django does not allow mutating fields since a change to a field of a model would lead to a database migration.

Nevertheless under the hood many fields use the same types and are basically replaceable. I.e. ImageField just stores a path to a string similar to what i CharField could do. Allthough the inner representation of data, or how the data is stored in the field might be different for some fields.

Still all of the fields come with a huge functionality and are usually deeply embedded and wired into the framework. Therefore django model fields are not generic. I guess your IDE is doing something, ... not appropriate :)

In the documentation you can find additional information on fields. Here you can find a list of all built-in fields.

edit: I was thinking some more about the issue. almost all fields, I believe all of them, extend the models.Field class. So this might be the reason your IDE is doing this. Some polymorphic thingy has been activated in the code generator or something.

CodePudding user response：

I think that the best way to type a field to get attribute hints (methods and attributes) of the value of the field and don't get linting errors when using strong or basic typing would be to use Union and do something like this:

username: str|CharField = CharField()