intorduce relation flags on basefield and simplify imports

ormar/relations/relation.py

@@ -1,17 +1,13 @@
 from enum import Enum
-from typing import List, Optional, Set, TYPE_CHECKING, Type, TypeVar, Union
+from typing import List, Optional, Set, TYPE_CHECKING, Type, Union
 
 import ormar  # noqa I100
 from ormar.exceptions import RelationshipInstanceError  # noqa I100
-from ormar.fields.foreign_key import ForeignKeyField  # noqa I100
 from ormar.relations.relation_proxy import RelationProxy
 
 if TYPE_CHECKING:  # pragma no cover
-    from ormar import Model
     from ormar.relations import RelationsManager
-    from ormar.models import NewBaseModel
-
-    T = TypeVar("T", bound=Model)
+    from ormar.models import Model, NewBaseModel, T
 
 
 class RelationType(Enum):
@@ -39,7 +35,7 @@ class Relation:
         manager: "RelationsManager",
         type_: RelationType,
         field_name: str,
-        to: Type["T"],
+        to: Type["Model"],
         through: Type["T"] = None,
     ) -> None:
         """
@@ -63,10 +59,10 @@ class Relation:
         self._owner: "Model" = manager.owner
         self._type: RelationType = type_
         self._to_remove: Set = set()
-        self.to: Type["T"] = to
-        self._through: Optional[Type["T"]] = through
+        self.to: Type["Model"] = to
+        self._through = through
         self.field_name: str = field_name
-        self.related_models: Optional[Union[RelationProxy, "T"]] = (
+        self.related_models: Optional[Union[RelationProxy, "Model"]] = (
             RelationProxy(relation=self, type_=type_, field_name=field_name)
             if type_ in (RelationType.REVERSE, RelationType.MULTIPLE)
             else None
@@ -161,7 +157,7 @@ class Relation:
                 self.related_models.pop(position)  # type: ignore
                 del self._owner.__dict__[relation_name][position]
 
-    def get(self) -> Optional[Union[List["T"], "T"]]:
+    def get(self) -> Optional[Union[List["Model"], "Model"]]:
         """
         Return the related model or models from RelationProxy.