Class NullType

lib/sqlalchemy/sql/sqltypes.py:3692–3742

An unknown type. :class:`.NullType` is used as a default type for those cases where a type cannot be determined, including: * During table reflection, when the type of a column is not recognized by the :class:`.Dialect` * When constructing SQL expressions using plain Python o

class NullType(TypeEngine[None]):
    """An unknown type.

    :class:`.NullType` is used as a default type for those cases where
    a type cannot be determined, including:

    * During table reflection, when the type of a column is not recognized
      by the :class:`.Dialect`
    * When constructing SQL expressions using plain Python objects of
      unknown types (e.g. ``somecolumn == my_special_object``)
    * When a new :class:`_schema.Column` is created,
      and the given type is passed
      as ``None`` or is not passed at all.

    The :class:`.NullType` can be used within SQL expression invocation
    without issue, it just has no behavior either at the expression
    construction level or at the bind-parameter/result processing level.
    :class:`.NullType` will result in a :exc:`.CompileError` if the compiler
    is asked to render the type itself, such as if it is used in a
    :func:`.cast` operation or within a schema creation operation such as that
    invoked by :meth:`_schema.MetaData.create_all` or the
    :class:`.CreateTable`
    construct.

    """

    __visit_name__ = "null"

    _isnull = True

    operator_classes = OperatorClass.ANY

    def literal_processor(self, dialect):
        return None

    class Comparator(TypeEngine.Comparator[_T]):
        __slots__ = ()

        def _adapt_expression(
            self,
            op: OperatorType,
            other_comparator: TypeEngine.Comparator[Any],
        ) -> Tuple[OperatorType, TypeEngine[Any]]:
            if isinstance(
                other_comparator, NullType.Comparator
            ) or not operators.is_commutative(op):
                return op, self.expr.type
            else:
                return other_comparator._adapt_expression(op, self)

    comparator_factory = Comparator


class TableValueType(HasCacheKey, TypeEngine[Any]):