pep484 ORM / SQL result support

after some experimentation it seems mypy is more amenable
to the generic types being fully integrated rather than
having separate spin-off types.   so key structures
like Result, Row, Select become generic.  For DML
Insert, Update, Delete, these are spun into type-specific
subclasses ReturningInsert, ReturningUpdate, ReturningDelete,
which is fine since the "row-ness" of these constructs
doesn't happen until returning() is called in any case.

a Tuple based model is then integrated so that these
objects can carry along information about their return
types.  Overloads at the .execute() level carry through
the Tuple from the invoked object to the result.

To suit the issue of AliasedClass generating attributes
that are dynamic, experimented with a custom subclass
AsAliased, but then just settled on having aliased()
lie to the type checker and return `Type[_O]`, essentially.
will need some type-related accessors for with_polymorphic()
also.

Additionally, identified an issue in Update when used
"mysql style" against a join(), it basically doesn't work
if asked to UPDATE two tables on the same column name.
added an error message to the specific condition where
it happens with a very non-specific error message that we
hit a thing we can't do right now, suggest multi-table
update as a possible cause.

Change-Id: I5eff7eefe1d6166ee74160b2785c5e6a81fa8b95

1 files changed, 5 insertions, 2 deletions

diff --git a/lib/sqlalchemy/orm/context.py b/lib/sqlalchemy/orm/context.py
index 4fee2d383..05287cbcf 100644
--- a/lib/sqlalchemy/orm/context.py
+++ b/lib/sqlalchemy/orm/context.py
@@ -17,6 +17,7 @@ from typing import Set
 from typing import Tuple
 from typing import Type
 from typing import TYPE_CHECKING
+from typing import TypeVar
 from typing import Union
 
 from . import attributes
@@ -48,14 +49,15 @@ from ..sql.base import _select_iterables
 from ..sql.base import CacheableOptions
 from ..sql.base import CompileState
 from ..sql.base import Executable
+from ..sql.base import Generative
 from ..sql.base import Options
 from ..sql.dml import UpdateBase
 from ..sql.elements import GroupedElement
 from ..sql.elements import TextClause
+from ..sql.selectable import ExecutableReturnsRows
 from ..sql.selectable import LABEL_STYLE_DISAMBIGUATE_ONLY
 from ..sql.selectable import LABEL_STYLE_NONE
 from ..sql.selectable import LABEL_STYLE_TABLENAME_PLUS_COL
-from ..sql.selectable import ReturnsRows
 from ..sql.selectable import Select
 from ..sql.selectable import SelectLabelStyle
 from ..sql.selectable import SelectState
@@ -72,6 +74,7 @@ if TYPE_CHECKING:
     from ..sql.selectable import SelectBase
     from ..sql.type_api import TypeEngine
 
+_T = TypeVar("_T", bound=Any)
 _path_registry = PathRegistry.root
 
 _EMPTY_DICT = util.immutabledict()
@@ -574,7 +577,7 @@ class ORMFromStatementCompileState(ORMCompileState):
         return None
 
 
-class FromStatement(GroupedElement, ReturnsRows, Executable):
+class FromStatement(GroupedElement, Generative, ExecutableReturnsRows):
     """Core construct that represents a load of ORM objects from various
     :class:`.ReturnsRows` and other classes including: