implement dataclass_transforms

Implement a new means of creating a mapped dataclass where
instead of applying the `@dataclass` decorator distinctly,
the declarative process itself can create the dataclass.

MapperProperty and MappedColumn objects themselves take
the place of the dataclasses.Field object when constructing
the class.

The overall approach is made possible at the typing level
using pep-681 dataclass transforms [1].

This new approach should be able to completely supersede the
previous "dataclasses" approach of embedding metadata into
Field() objects, which remains a mutually exclusive declarative
setup style (mixing them introduces new issues that are not worth
solving).

[1] https://peps.python.org/pep-0681/#transform-descriptor-types-example

Fixes: #7642
Change-Id: I6ba88a87c5df38270317b4faf085904d91c8a63c

1 files changed, 14 insertions, 12 deletions

diff --git a/lib/sqlalchemy/orm/relationships.py b/lib/sqlalchemy/orm/relationships.py
index 1186f0f54..deaf52147 100644
--- a/lib/sqlalchemy/orm/relationships.py
+++ b/lib/sqlalchemy/orm/relationships.py
@@ -49,6 +49,7 @@ from .base import class_mapper
 from .base import LoaderCallableStatus
 from .base import PassiveFlag
 from .base import state_str
+from .interfaces import _AttributeOptions
 from .interfaces import _IntrospectsAnnotations
 from .interfaces import MANYTOMANY
 from .interfaces import MANYTOONE
@@ -56,7 +57,6 @@ from .interfaces import ONETOMANY
 from .interfaces import PropComparator
 from .interfaces import RelationshipDirection
 from .interfaces import StrategizedProperty
-from .util import _extract_mapped_subtype
 from .util import _orm_annotate
 from .util import _orm_deannotate
 from .util import CascadeOptions
@@ -355,6 +355,7 @@ class Relationship(
         post_update: bool = False,
         cascade: str = "save-update, merge",
         viewonly: bool = False,
+        attribute_options: Optional[_AttributeOptions] = None,
         lazy: _LazyLoadArgumentType = "select",
         passive_deletes: Union[Literal["all"], bool] = False,
         passive_updates: bool = True,
@@ -380,7 +381,7 @@ class Relationship(
         _local_remote_pairs: Optional[_ColumnPairs] = None,
         _legacy_inactive_history_style: bool = False,
     ):
-        super(Relationship, self).__init__()
+        super(Relationship, self).__init__(attribute_options=attribute_options)
 
         self.uselist = uselist
         self.argument = argument
@@ -1701,18 +1702,19 @@ class Relationship(
         cls: Type[Any],
         key: str,
         annotation: Optional[_AnnotationScanType],
+        extracted_mapped_annotation: Optional[_AnnotationScanType],
         is_dataclass_field: bool,
     ) -> None:
-        argument = _extract_mapped_subtype(
-            annotation,
-            cls,
-            key,
-            Relationship,
-            self.argument is None,
-            is_dataclass_field,
-        )
-        if argument is None:
-            return
+        argument = extracted_mapped_annotation
+
+        if extracted_mapped_annotation is None:
+
+            if self.argument is None:
+                self._raise_for_required(key, cls)
+            else:
+                return
+
+        argument = extracted_mapped_annotation
 
         if hasattr(argument, "__origin__"):