Help with using custom types (TypesDecorator)

[madduck]

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Example Code

from typing import Any

from pydantic import GetCoreSchemaHandler
from pydantic_core import CoreSchema, core_schema
from sqlmodel import (
    Field,
    Integer,
    SQLModel,
    Session,
    TypeDecorator,
    create_engine,
    select,
)


class IntWhereZeroIsNone(int):
    @staticmethod
    def validator(value: int | None) -> int | None:
        return value if value != 0 else None

    @classmethod
    def __get_pydantic_core_schema__(
        cls, source_type: Any, handler: GetCoreSchemaHandler
    ) -> CoreSchema:
        return core_schema.no_info_after_validator_function(cls.validator, handler(int))


class IntWhereZeroIsNoneType(IntWhereZeroIsNone, TypeDecorator):
    impl = Integer

    def process_bind_param(self, value: int | None, dialect: Any) -> int | None:
        return self.validator(value)


class MyModel(SQLModel, table=True):
    x: IntWhereZeroIsNoneType = Field(default=None, primary_key=True, sa_type=Integer)


m = MyModel(x=1)
assert m.x == 1
m = MyModel(x=0)
assert m.x is None


engine = create_engine("sqlite:///")

with Session(engine) as session:
    session.add(MyModel(x=0))
    session.add(MyModel(x=None))
    session.commit()

    for row in session.exec(select(MyModel)):
        assert row.x is None

Description

When I look at this code, it seems straight-forward. The linters and type checkers complain about assigning None to x but more importantly, assert m.x is None fails.

This is a silly example: an int field that is None instead of 0 and otherwise just an int, but I am wondering how to get there.

How would you do it?

Operating System

Linux, Windows, macOS, Other

Operating System Details

No response

SQLModel Version

0.0.24

Python Version

3.13.3

Additional Context

No response