✨ Increase `number_of_types` to 5 to support longer select queries

[GiorgioPorgio]

I am trying to write a select statement that selects 5 different SQLModel children. However I get a type error as the overloads for select are limited to 4.

Increasing to 6+ causes mypy to hang, so I chose 5 :)

Resolves https://github.com/fastapi/sqlmodel/issues/271#issuecomment-2332795054

Thank you very much for your time and working on OSS!

[YuriiMotov]

Just as an idea: what if we introduce a rule that all _TScalar_XX should go before any of _TCCA[_TXX]? This way we only need to add 7 overloads for the 5 parameters, 8 overloads for 6 parameters, etc..

See example for 5 parameters in the details:

@overload
def select(  # type: ignore
    __ent0: _TCCA[_T0],
    __ent1: _TCCA[_T1],
    __ent2: _TCCA[_T2],
    __ent3: _TCCA[_T3],
    __ent4: _TCCA[_T4],
) -> Select[Tuple[_T0, _T1, _T2, _T3, _T4]]: ...


@overload
def select(  # type: ignore
    entity_0: _TScalar_0,
    __ent1: _TCCA[_T1],
    __ent2: _TCCA[_T2],
    __ent3: _TCCA[_T3],
    __ent4: _TCCA[_T4],
) -> Select[Tuple[_TScalar_0, _T1, _T2, _T3, _T4]]: ...


@overload
def select(  # type: ignore
    entity_0: _TScalar_0,
    entity_1: _TScalar_1,
    __ent2: _TCCA[_T2],
    __ent3: _TCCA[_T3],
    __ent4: _TCCA[_T4],
) -> Select[Tuple[_TScalar_0, _TScalar_1, _T2, _T3, _T4]]: ...


@overload
def select(  # type: ignore
    entity_0: _TScalar_0,
    entity_1: _TScalar_1,
    entity_2: _TScalar_2,
    __ent3: _TCCA[_T3],
    __ent4: _TCCA[_T4],
) -> Select[Tuple[_TScalar_0, _TScalar_1, _TScalar_2, _T3, _T4]]: ...


@overload
def select(  # type: ignore
    entity_0: _TScalar_0,
    entity_1: _TScalar_1,
    entity_2: _TScalar_2,
    entity_3: _TScalar_3,
    __ent4: _TCCA[_T4],
) -> Select[Tuple[_TScalar_0, _TScalar_1, _TScalar_2, _TScalar_3, _T4]]: ...


@overload
def select(  # type: ignore
    entity_0: _TScalar_0,
    entity_1: _TScalar_1,
    entity_2: _TScalar_2,
    entity_3: _TScalar_3,
    entity_4: _TScalar_4,
) -> Select[Tuple[_TScalar_0, _TScalar_1, _TScalar_2, _TScalar_3, _TScalar_4]]: ...


@overload
@deprecated(
    """
    This version of `select` function is deprecated.
    You should order parameters so that all `_TScalar_XX` parameters would go before any
    of `_TCCA[_TXX]` parameter.

    Read more: [link to the documentation]
    """
)
def select(  # type: ignore
    __ent0: _TCCA[_T0],
    param_1: Any,
    param_2: Any,
    param_3: Any,
    param_4: Any,
) -> Select[Tuple[_T0, Any, Any, Any, Any]]: ...

Last overload is to catch the wrong parameters order and show the deprecation warning with clear message and link to the docs.

We can leave overloads for 1-4 parameters as it is for backward compatibility, or optionally mark overloads that don't follow this rule as deprecated.

[dtip]

Increasing the limit from 4 to 5 means this problem will happen again when someone has a select with 6 inputs. I'm not familiar with the code at all, but is there some way to accept an arbitrarily large number of inputs? Or increase the limit to something absurd like 50?

[GiorgioPorgio]

is there some way to accept an arbitrarily large number of inputs? Or increase the limit to something absurd like 50?

Unfortunately no. Because of limitations of Python typing regarding order of generic types, you have to explicitly specify every possible combination, leading to a factorial explosion.

@YuriiMotov 's solution could work perhaps, have not tested it and Python is not my main laguage. I think both solutions would help the community.

I acknowledge the current PR is more of a quick win but a safe change that would improve DX.