sqlmodel: several bugfixes

These were found by testing a more comprehensive use case:

https://github.com/adsharma/fastapi-shopping/blob/main/models.py

fquery/sqlmodel.py

@@ -64,7 +64,7 @@ def many_to_one(key_column=None, back_populates=None):
     if key_column is not None:
         ret.metadata["SQL"]["key_column"] = key_column
     if back_populates is not None:
-        ret.metadata["SQL"][back_populates] = back_populates
+        ret.metadata["SQL"]["back_populates"] = back_populates
     return ret
 
 
@@ -134,8 +134,13 @@ def get_field_type(field, cls):
             type_class = field.type
             other_class = type_class.__args__[0]
             if has_many_to_one_relationship:
-                type_class = get_type_hints(cls)[field.name]
-                return Optional[other_class.__sqlmodel__]
+                try:
+                    type_class = get_type_hints(cls)[field.name]
+                except NameError:
+                    # TODO: log exception?
+                    pass
+                else:
+                    return Optional[other_class.__sqlmodel__]
         return field.type
 
     def patch_back_populates_types(field, back_populates, cls, sqlmodel_cls):
@@ -145,7 +150,16 @@ def patch_back_populates_types(field, back_populates, cls, sqlmodel_cls):
         if has_relationship:
             if has_many_to_one_relationship:
                 type_class = field.type
-                other_class = type_class.__args__[0].__sqlmodel__
+                try:
+                    type_class = get_type_hints(cls)[field.name]
+                except NameError:
+                    # TODO: log exception?
+                    pass
+                inner = type_class.__args__[0]
+                if isinstance(inner, ForwardRef):
+                    # can't patch right now. Try at a later time via back_populates
+                    return
+                other_class = inner.__sqlmodel__
                 old = other_class.__annotations__[back_populates]
                 # Should be sqlalchemy.orm.base.Mapped[typing.List[ForwardRef('T')]]
                 # replace it with Mapped[List[sqlmodel_cls]]
@@ -156,17 +170,23 @@ def patch_back_populates_types(field, back_populates, cls, sqlmodel_cls):
                         List[sqlmodel_cls]
                     ]
                     other_class.sqlmodel_rebuild()
-            else:
-                # Replace Optional['T'] with Optional[TSQLModel]
-                old = field.type
-                origin = get_origin(old)
-                inner = get_args(old)
-                if (
-                    origin == Union
-                    and len(inner)
-                    and inner[0] == ForwardRef(cls.__name__)
-                ):
-                    sqlmodel_cls.__annotations__[field.name] = Optional[sqlmodel_cls]
+
+        # Replace Optional['T'] with Optional[TSQLModel]
+        old = field.type
+        origin = get_origin(old)
+        inner = get_args(old)
+        needs_rebuild = False
+        if origin == Union and len(inner) and inner[0] == ForwardRef(cls.__name__):
+            sqlmodel_cls.__annotations__[field.name] = Optional[sqlmodel_cls]
+            needs_rebuild = True
+
+        # Replace Optional[T] with Optional[TSQLModel] if T is a dataclass
+        if origin == Union and len(inner) and is_dataclass(inner[0]):
+            sqlmodel_cls.__annotations__[field.name] = Optional[inner[0].__sqlmodel__]
+            needs_rebuild = True
+
+        if needs_rebuild:
+            sqlmodel_cls.sqlmodel_rebuild()
 
     def default_table_name(clsname: str) -> str:
         return inflection.underscore(inflection.pluralize(clsname))