Add Executable to DefaultGenerator

Fixed the class hierarchy for the :class:`_schema.Sequence` and the more
general :class:`_schema.DefaultGenerator` base, as these are "executable"
as statements they need to include :class:`_sql.Executable` in their
hierarchy, not just :class:`_roles.StatementRole` as was applied
arbitrarily to :class:`_schema.Sequence` previously. The fix allows
:class:`_schema.Sequence` to work in all ``.execute()`` methods including
with :meth:`_orm.Session.execute` which was not working in the case that a
``do_orm_execute()`` handler was also established.

Fixes: #6668
Change-Id: I0d192258c7cbd1bce2552f9e748e8fdd680dc45f

1 files changed, 3 insertions, 2 deletions

diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py
index 221d49db9..484cdddc8 100644
--- a/lib/sqlalchemy/sql/schema.py
+++ b/lib/sqlalchemy/sql/schema.py
@@ -41,6 +41,7 @@ from . import visitors
 from .base import _bind_or_error
 from .base import DedupeColumnCollection
 from .base import DialectKWArgs
+from .base import Executable
 from .base import SchemaEventTarget
 from .coercions import _document_text_coercion
 from .elements import ClauseElement
@@ -2464,7 +2465,7 @@ class ForeignKey(DialectKWArgs, SchemaItem):
             self._set_target_column(_column)
 
 
-class DefaultGenerator(SchemaItem):
+class DefaultGenerator(Executable, SchemaItem):
     """Base class for column *default* values."""
 
     __visit_name__ = "default_generator"
@@ -2678,7 +2679,7 @@ class IdentityOptions(object):
         self.order = order
 
 
-class Sequence(IdentityOptions, roles.StatementRole, DefaultGenerator):
+class Sequence(IdentityOptions, DefaultGenerator):
     """Represents a named database sequence.
 
     The :class:`.Sequence` object represents the name and configurational