Method _join_condition

lib/sqlalchemy/sql/selectable.py:1420–1462

Create a join condition between two tables or selectables. See sqlalchemy.sql.util.join_condition() for full docs.

(
        cls,
        a: FromClause,
        b: FromClause,
        *,
        a_subset: Optional[FromClause] = None,
        consider_as_foreign_keys: Optional[
            AbstractSet[ColumnClause[Any]]
        ] = None,
    )

    @classmethod
    def _join_condition(
        cls,
        a: FromClause,
        b: FromClause,
        *,
        a_subset: Optional[FromClause] = None,
        consider_as_foreign_keys: Optional[
            AbstractSet[ColumnClause[Any]]
        ] = None,
    ) -> ColumnElement[bool]:
        """Create a join condition between two tables or selectables.

        See sqlalchemy.sql.util.join_condition() for full docs.

        """
        constraints = cls._joincond_scan_left_right(
            a, a_subset, b, consider_as_foreign_keys
        )

        if len(constraints) > 1:
            cls._joincond_trim_constraints(
                a, b, constraints, consider_as_foreign_keys
            )

        if len(constraints) == 0:
            if isinstance(b, FromGrouping):
                hint = (
                    " Perhaps you meant to convert the right side to a "
                    "subquery using alias()?"
                )
            else:
                hint = ""
            raise exc.NoForeignKeysError(
                "Can't find any foreign key relationships "
                "between '%s' and '%s'.%s"
                % (a.description, b.description, hint)
            )

        crit = [(x == y) for x, y in list(constraints.values())[0]]
        if len(crit) == 1:
            return crit[0]
        else:
            return and_(*crit)

    @classmethod
    def _can_join(