Express a foreign key directly with the model

[ZeeD]

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Example Code

from sqlmodel import Field, SQLModel

class Foo(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)

class Current(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    foo_id: int = Field(foreign_key='foo.id')

class Desiderata(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    foo_id: int = Field(foreign_key=Foo.id)

Description

At the moment, in a 1-to-many scenario, if I want to create a foreign key, I need to specify it with a string. (the Current class in the example)
I would like to do it passing "directly" the field (the Desiderata).

Keep in mind that I want to support both ways, I know there are cases when the relationship is not so simple, but I would like to have the simple case (that is the most common in my experience) to just be simpler

FWIW at the moment I have a very simple function that offer me this kind of behavior:

def fk(col: int) -> str:
    attr = cast(QueryableAttribute[Any], col)
    return f'{attr.class_.__tablename__}.{attr.key}'

but I would like to have this supported natively.

As an addendum: now the Desiderata class raises an AssertionError (as there is an assert isinstance(foreign_key, str)) so this change shouldn't create any kind of back compatibility

Operating System

macOS

Operating System Details

No response

SQLModel Version

0.0.14

Python Version

3.12

Additional Context

No response