fix for #226

ormar/models/helpers/sqlalchemy.py

@@ -2,6 +2,7 @@ import logging
 from typing import Dict, List, Optional, TYPE_CHECKING, Tuple, Type, Union
 
 import sqlalchemy
+from pydantic.typing import ForwardRef
 
 import ormar  # noqa: I100, I202
 from ormar.models.descriptors import RelationDescriptor
@@ -203,7 +204,7 @@ def _is_through_model_not_set(field: "BaseField") -> bool:
     :return: result of the check
     :rtype: bool
     """
-    return field.is_multi and not field.through
+    return field.is_multi and not field.through and not field.to.__class__ == ForwardRef
 
 
 def _is_db_field(field: "BaseField") -> bool:

ormar/models/newbasemodel.py

@@ -447,6 +447,9 @@ class NewBaseModel(pydantic.BaseModel, ModelTableProxy, metaclass=ModelMetaclass
                 field = cast(ForeignKeyField, field)
                 field.evaluate_forward_ref(globalns=globalns, localns=localns)
                 field.set_self_reference_flag()
+                if field.is_multi and not field.through:
+                    field = cast(ormar.ManyToManyField, field)
+                    field.create_default_through_model()
                 expand_reverse_relationship(model_field=field)
                 register_relation_in_alias_manager(field=field)
                 update_column_definition(model=cls, field=field)