Fix #1399 - skip expanding through fields on clone (#1407)

* Fix #1399

* run db

ormar/models/helpers/relations.py

@@ -91,7 +91,11 @@ def expand_reverse_relationships(model: Type["Model"]) -> None:
     """
     model_fields = list(model.ormar_config.model_fields.values())
     for model_field in model_fields:
-        if model_field.is_relation and not model_field.has_unresolved_forward_refs():
+        if (
+            model_field.is_relation
+            and not model_field.has_unresolved_forward_refs()
+            and not model_field.is_through
+        ):
             model_field = cast("ForeignKeyField", model_field)
             expand_reverse_relationship(model_field=model_field)
 

tests/test_model_definition/test_through_model_relation_setup_on_clone.py

@@ -0,0 +1,34 @@
+import ormar
+import pytest
+
+from tests.lifespan import init_tests
+from tests.settings import create_config
+
+base_ormar_config = create_config()
+
+
+class Author(ormar.Model):
+    ormar_config = base_ormar_config.copy(tablename="authors")
+
+    id = ormar.Integer(primary_key=True)
+    name = ormar.String(max_length=100)
+
+
+class Book(ormar.Model):
+    ormar_config = base_ormar_config.copy(tablename="books")
+
+    id = ormar.Integer(primary_key=True)
+    title = ormar.String(max_length=100)
+    author = ormar.ManyToMany(
+        Author,
+    )
+    year = ormar.Integer(nullable=True)
+
+
+create_test_database = init_tests(base_ormar_config)
+
+
+@pytest.mark.asyncio
+async def test_tables_are_created():
+    async with base_ormar_config.database:
+        assert await Book.objects.all() == []