✨ Support Annotated approach for Relationship attributes

[bolu61]

see #229 (comment)

I'm not really sure how Pydantic does it, but here's a potential workaround to the problem.

[YuriiMotov]

@bolu61, thanks for working on this!

So, this PR fixes the following code example:

class Foo(SQLModel, table=True):
    id: Annotated[int | None, Field(primary_key=True)] = None
    uuid: Annotated[UUID, Field(unique=True)]

class Bar(SQLModel, table=True):
    id: Annotated[int | None, Field(primary_key=True)] = None
    uuid: Annotated[UUID, Field(unique=True)]
    foo_id: Annotated[int, Field(foreign_key="foo.id")]
    foo: Annotated[Foo, Relationship()]

For now last line (with Relationship()) doesn't work (ValueError: <class '__main__.Foo'> has no matching SQLAlchemy type) and this PR fixes that.

I think this is not the same that was initially proposed in #229. The idea there was to support passing multiple annotations like:

class Hero(SQLModel, table=True):
    id: Annotated[Optional[int], Field(examples=....), Column(primary_key=True)] = None

Where Field can be pydantic.Field.
So, I suggest we unmark this PR as the one that resolves that issue.

As for changes introduced by this PR, I think it goes in line with modern recommendations to use Annotated approach instead parameterizing fields via default value.
I think we should test this approach more and add some automatic tests. Then it will have all chances to be accepted.

[bolu61]

@YuriiMotov I agree.

I'm not too familiar with this codebase. Can you point me to where I can write those tests?

[YuriiMotov]

I'm not too familiar with this codebase. Can you point me to where I can write those tests?

You can create an annotated version of the code example from "Relationships" section of docs:

• Go to https://github.com/fastapi/sqlmodel/tree/main/docs_src/tutorial/relationship_attributes/define_relationship_attributes
• Create a copy of tutorial001_py310.py, call it tutorial001_an_py310.py
• Edit code to follow the Annotated approach
• Go to https://github.com/fastapi/sqlmodel/tree/main/tests/test_tutorial/test_relationship_attributes/test_define_relationship_attributes
• Create a copy of test_tutorial001_py310.py, call it test_tutorial001_an_py310.py
• Update code to import app from tutorial001_an_py310.py
• Push changes and check that new version of code example appeared in "Other versions and variants"

[github-actions]

📝 Docs preview

Last commit 252b444 at: https://a151d4e3.sqlmodel.pages.dev

[svlandeg]

The test that was failing previously is now fixed thanks to #1607.

@YuriiMotov : do you want to give this another review?

[YuriiMotov]

This needs some more work and testing..

@bolu61, would you like to continue working on this?

[YuriiMotov]

This is incorrect:

• at least it should be elif origin is Annotated: to avoid double-wrapping already Mapped annotations
• Also, it would fail for Annotated[Mapped[T], ...] (would add one more Mapped)

[YuriiMotov]

This will only find relationships with default value, but will not work for fields like heroes: Annotated[list["Hero"], Relationship(back_populates="team")].
Such annotations are not typing-friendly (will be treated as required fields), but we should probably still support them..

Also, note that this way we drop the default value in case of Annotated relationship (team: Annotated[Team | None, Relationship(back_populates="heroes")] = None - whatever you specify as default value, it will be just dropped)

[bolu61]

Ofc. Might take me some time to reread the rest of the code though.