I have the following project hierarchy

src/
   schemas/
          foo.py
          bar.py
   models/
         foo.py
         bar.py

models has definitions for SQLAlchemy classes

#foo.py

from typing import TYPE_CHECKING
if TYPE_CHECKING:
    from src.models.bar import Bar
class Foo(Base):
    x: Mapped[int] = mapped_column(Integer)
    y: Mapped["Bar"] = relationship("Bar", back_populates="b")

#bar.py

from typing import TYPE_CHECKING
if TYPE_CHECKING:
    from src.models.foo import Foo
class Bar(Base):
    a: Mapped[int] = mapped_column(Integer)
    b: Mapped["Foo"] = relationship("Foo", back_populates="y")

schemas has definations for Pydantic classes

#foo.py

from pydantic import BaseModel, Field, field_validator
from typing import TYPE_CHECKING
if TYPE_CHECKING:
    from src.schemas.bar import Bar

class Foo(BaseModel):
    x: int = Field(...)
    y: "Bar" = Field(...)


# bar.py

from pydantic import BaseModel, Field, field_validator
from typing import TYPE_CHECKING
if TYPE_CHECKING:
    from src.schemas.foo import Foo
class Bar(BaseModel):
    a: int = Field(...)
    b: "Foo" = Field(...)

The issue I am facing is in validating relationship field.

#foo.py

from pydantic import BaseModel, Field, field_validator
from typing import TYPE_CHECKING
if TYPE_CHECKING:
    from src.schemas.bar import Bar

class Foo(BaseModel):
    x: int = Field(...)
    y: "Bar" = Field(...)
    @field_validator("y", mode="before")
    @classmethod
    def validate_relationship(cls, v: Any):
        return Bar.model_validate(v)

# bar.py

from pydantic import BaseModel, Field, field_validator
from typing import TYPE_CHECKING
if TYPE_CHECKING:
    from src.schemas.foo import Foo
class Bar(BaseModel):
    a: int = Field(...)
    b: "Foo" = Field(...)
    @field_validator("b", mode="before")
    @classmethod
    def validate_relationship(cls, v: Any):
        return Bar.model_validate(v)

I get the NameError ‘Bar’ when validating Foo and NameError ‘Foo’ when validating ‘Bar

How do I resolve this error without running into circular imports

I have defined TYPE_CHECKING import guards, importing annotations from futures package lazy loading of modules.