What does it mean "to=" when creating model field in django?

Question

Are those tree ways giving the same result/field, is there any other way?

    class Message(models.Model):
        user = models.ForeignKey(to=User)

        user = models.ForeignKey(User)

        user = models.ForeignKey("User")

Answer 1

Are those tree ways giving the same result/field

Yes, although the first requires to import a model named user, and is thus vulnerable to cyclic imports.

is there any other way?

The advised way is to make use of the settings.AUTH_USER_MODEL ^[Django-doc] to refer to the user model, than to use the User model ^[Django-doc] directly, so:

from django.conf import settings


class Message(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)

For more information you can see the referencing the User model section of the documentation.