Class InstrumentedAttribute

lib/sqlalchemy/orm/attributes.py:515–575

Class bound instrumented attribute which adds basic :term:`descriptor` methods. See :class:`.QueryableAttribute` for a description of most features.

class InstrumentedAttribute(QueryableAttribute[_T_co]):
    """Class bound instrumented attribute which adds basic
    :term:`descriptor` methods.

    See :class:`.QueryableAttribute` for a description of most features.


    """

    __slots__ = ()

    inherit_cache = True
    """:meta private:"""

    # hack to make __doc__ writeable on instances of
    # InstrumentedAttribute, while still keeping classlevel
    # __doc__ correct

    @util.rw_hybridproperty
    def __doc__(self) -> Optional[str]:
        return self._doc

    @__doc__.setter  # type: ignore
    def __doc__(self, value: Optional[str]) -> None:
        self._doc = value

    @__doc__.classlevel  # type: ignore
    def __doc__(cls) -> Optional[str]:
        return super().__doc__

    def __set__(self, instance: object, value: Any) -> None:
        self.impl.set(
            instance_state(instance), instance_dict(instance), value, None
        )

    def __delete__(self, instance: object) -> None:
        self.impl.delete(instance_state(instance), instance_dict(instance))

    @overload
    def __get__(
        self, instance: None, owner: Any
    ) -> InstrumentedAttribute[_T_co]: ...

    @overload
    def __get__(self, instance: object, owner: Any) -> _T_co: ...

    def __get__(
        self, instance: Optional[object], owner: Any
    ) -> Union[InstrumentedAttribute[_T_co], _T_co]:
        if instance is None:
            return self

        dict_ = instance_dict(instance)
        if self.impl.supports_population and self.key in dict_:
            return dict_[self.key]  # type: ignore[no-any-return]
        else:
            try:
                state = instance_state(instance)