✨ Support sqlalchemy MappedColumn

[spazm]

Reopening PR #896.

id: Optional[int] = Field(default=None, sa_column=mapped_column('id', Integer, primary_key=True))

This PR adds a test with sqlmodel.orm.mapped_column working for sa_column. This test fails on current main.

from typing import Optional
from sqlalchemy import Integer
from sqlalchemy.orm import mapped_column
from sqlmodel import Field

class Foo(SqlModel):
    id: Optional[int] = Field(default=None, sa_column=mapped_column('id', Integer, primary_key=True))

[spazm]

This PR is failing one test because it does not have a label assigned.
How do I get a label assigned?

Do I need to open a separate issue to point to the PR?

[lachaib]

Hello,

While trying to fix a problem probably similar to yours (I want to make a column deferrable but it can only be made on mapped_column and not on Column), I tested a simpler solution:

at the end of get_column_from_field, I returned mapped_column instead of Column, hence the deferred keyword can be passed as sa_column_kwargs

According to tests, this is fully compatible. Also it's slightly more readable:

not_loaded: str = Field(sa_column_kwargs={"deferred": True})
# vs
not_loaded: str = Field(sa_type=mapped_column(String, deferred=True))

Maybe there's an underlying reason why this cannot be acceptable but I think it's worth sharing (and also will help me follow this pull request)