some further cleanup and optim

ormar/fields/base.py

@@ -5,6 +5,7 @@ import sqlalchemy
 from pydantic import Field, typing
 from pydantic.fields import FieldInfo
 
+import ormar # noqa I101
 from ormar import ModelDefinitionError  # noqa I101
 
 if TYPE_CHECKING:  # pragma no cover
@@ -34,6 +35,10 @@ class BaseField(FieldInfo):
     default: Any
     server_default: Any
 
+    @classmethod
+    def is_valid_uni_relation(cls) -> bool:
+        return not issubclass(cls, ormar.fields.ManyToManyField) and not cls.virtual
+
     @classmethod
     def get_alias(cls) -> str:
         return cls.alias if cls.alias else cls.name