Method _sentinel_column_characteristics

lib/sqlalchemy/sql/schema.py:1216–1363

determine a candidate column (or columns, in case of a client generated composite primary key) which can be used as an "insert sentinel" for an INSERT statement. The returned structure, :class:`_SentinelColumnCharacterization`, includes all the details needed by :cla

(
        self,
    )

    @util.ro_memoized_property
    def _sentinel_column_characteristics(
        self,
    ) -> _SentinelColumnCharacterization:
        """determine a candidate column (or columns, in case of a client
        generated composite primary key) which can be used as an
        "insert sentinel" for an INSERT statement.

        The returned structure, :class:`_SentinelColumnCharacterization`,
        includes all the details needed by :class:`.Dialect` and
        :class:`.SQLCompiler` to determine if these column(s) can be used
        as an INSERT..RETURNING sentinel for a particular database
        dialect.

        .. versionadded:: 2.0.10

        """

        sentinel_is_explicit = False
        sentinel_is_autoinc = False
        the_sentinel: Optional[_typing_Sequence[Column[Any]]] = None

        # see if a column was explicitly marked "insert_sentinel=True".
        explicit_sentinel_col = self._sentinel_column

        if explicit_sentinel_col is not None:
            the_sentinel = (explicit_sentinel_col,)
            sentinel_is_explicit = True

        autoinc_col = self._autoincrement_column
        if sentinel_is_explicit and explicit_sentinel_col is autoinc_col:
            assert autoinc_col is not None
            sentinel_is_autoinc = True
        elif explicit_sentinel_col is None and autoinc_col is not None:
            the_sentinel = (autoinc_col,)
            sentinel_is_autoinc = True

        default_characterization = _SentinelDefaultCharacterization.UNKNOWN

        if the_sentinel:
            the_sentinel_zero = the_sentinel[0]
            if the_sentinel_zero.identity:
                if the_sentinel_zero.identity._increment_is_negative:
                    if sentinel_is_explicit:
                        raise exc.InvalidRequestError(
                            "Can't use IDENTITY default with negative "
                            "increment as an explicit sentinel column"
                        )
                    else:
                        if sentinel_is_autoinc:
                            autoinc_col = None
                            sentinel_is_autoinc = False
                        the_sentinel = None
                else:
                    default_characterization = (
                        _SentinelDefaultCharacterization.IDENTITY
                    )
            elif (
                the_sentinel_zero.default is None